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Airgun Moderator Design, Performance, and Development - THE BIG TEST (part 5)

Silent Thunder Ordnance

Going from left to right, back to front, we have Wolf Air?, Neil Clague, Neil Clague, 0dB, TKO?, STO Mus, STO Pilum, DonnyFL Sumo, Wolf Air?, DonnyFL Tanto, DonnyFL FX, STO Levitas, and Huggett Belita.

Going from left to right, back to front, we have Wolf Air?, Neil Clague, Neil Clague, 0dB, TKO?, STO Mus, STO Pilum, DonnyFL Sumo, Wolf Air?, DonnyFL Tanto, DonnyFL FX, STO Levitas, and Huggett Belita.

If you missed it, you can catch part 4 here.

First off is an immense thank you to the half dozen or so trusting souls who sent me, a total stranger, what I have to imagine is well over a grand worth of airgun moderators. You guys are the heroes of this story as far as I'm concerned. Don't be shy to sound off if you want to take some public karma, but out of respect for your privacy and a potential desire to avoid any backlash I've intentionally avoided publicly naming any of you.

So I want to preface this with a dozen different points before diving into the meat of things. I also want to summarize the test protocol, add a few important caveats, and generally reiterate a few things. Feel free to skip this section if you just want the results, but if you have questions you might want to revisit this section before asking because I might just have already covered it. ;)

One of my best friends is SUPER into this, and when he heard that I was getting together other moderators he insisted on getting involved. I think it was something more along the lines of “your design sucks, you have no idea what you're doing, I can beat you at this.” The two of us spent a weekend in an incredibly crappy and hastily thrown together anechoic chamber (which really wasn't) rapid-prototyping, testing, eating cold pizza, arguing, tweaking designs, accusing the other of stealing ideas, rinse, repeat, etc., ad nauseum. By the time the weekend was over we'd both eaten some humble pie, learned a lot, tipped a few sacred cows (both our own and other people's), and improved moderator performance beyond what either of us had thought possible. (and it was a lot compared to my previous design) All of this was still done within my original 35x120mm envelope, which is cursedly small in terms of trying to cram things in, but means revisions can be cracked out much faster than a larger design...... and believe me, I know, because after this was done, for the sake of humor, I scaled the design up just to see what'd happen. It doesn't really stand to reason that a good small design would scale to a big one, but at least some of the principles you'd assume would be maintained..... right?

Next bullet point I want to make is that nobody has paid me a penny to test any of these designs, nor were any of them sent by the manufacturer, at least not to my knowledge. I also don't have a bone to pick with any company that manufacturers moderators. My subjective qualitative observations on cans, both sound and manufacturer design/quality, are based nothing other than my own eyeballs and earballs. Take them for what little they're worth, which is to say the deranged ramblings of some random guy on the internets.

Accuracy vs. precision is something that came up in an unfortunately contentious manner in another thread. Without intending to upset anyone, this discussion helped me put my finger on something I wanted to say about the test equipment I'm using to do this work. To define the two terms with an analogy, an accurate gun is one which will put the rounds around the bullseye, while a precise one may put the rounds nowhere near the point of aim, but it puts them all together in a close group. The reason why the numbers I list aren't in decibels is because I can measure the sound with a good level of precision, however I'm unsure of the accuracy therefore do not want to mislead by claiming the center of the target is somewhere that it is not. Each data sampling is actually done on multiple simultaneous pickups. You can see these as different colors in each image. This acts as a check on every single shot, if the two pickups disagree (rare) something clearly went wrong and I just repeat that shot. And there are multiple shots taken (five) for each test. In this way every shot is double-checked, and is an average of an average. All this, plus a little knowledge of the system, gives me a good confidence interval on the precision of the data recorded.

The subjective ear is a tricky thing. I can empirically say which moderator is louder or quieter at it's peak, and this is the standard in the firearm suppressor industry, however this alone is NOT a strictly accurate reflection of how a person will perceive the loudness of the moderator or firearm suppressor for that matter. Particularly at close range, moderators with a lower peak but which produce more noise subsequent may sound louder. Different frequencies will also sound louder, and which frequencies these are will vary between people. This is part of why I feel it is so important to post an image of the sound profile, it gives a more complete glimpse into what the moderator is doing. To the greatest extent reasonable I've striven to blind myself while doing this testing, so I can write my thoughts on how I think each moderator sounded before diving into the numbers and sound profiles. It is an imperfect way of doing things, but I also consider my subjective observations to be secondary to the hard data.

Something brought up by another member is frequency, and that this frequency will change with moderator volume. Each vertical line represents a millisecond, so you're all welcome to do a little napkin math and see how you think the predominant frequency changes between moderators. I've not correlated any of this to perception, so what exactly it means is hard to say. Obviously there are multiple frequencies going on here, and the visible snapshot is quite short.

I expect, but have no data to support, that there may be differing relative performance between moderators on different hosts. Why? Because of the differing nature of the volume of air and sound they produce. A very small sound-damping focused moderator may perform very well on a low output target gun, better than a really really big high power moderator. But you wouldn't expect that tiny moderator to still be better if you put it on an Airforce Texan right? What is important here is that both moderators will be louder than before, but their relative positions of which is less loud will likely have changed. At this point it is purely a thought experiment, because I don't have a vastly more powerful airgun to test. It is also worth noting though that all the moderators here are made for small-bore use (being defined as sub-100 foot pounds and .30 caliber or less) and most attach via 1/2-20UNF. My host, an FX Crown, is running about 32 foot pounds in this test. This puts it in roughly the same power class as almost all use cases for these moderators. Even if we take the “extreme” end of the spectrum, such as an FX Wildcat II .30 cal with its 700mm barrel, that only puts out 69 foot pounds (ref. Utah Airguns' product listing). Or, put another way, if you look at a Utah Airguns caliber chart on the FX ImpactX page, you'll see the comparative shot count between 22, 25, and 30 caliber. The 30s seem to run about half the shot count of the 22s, suggesting twice the air consumption. I would therefore put those in roughly the same ballpark, as opposed to “big bores” which may output an order of magnitude greater air. Looking at the forums we mostly seem to be shooting 22s and 25s, which are maybe 25% different in terms of air consumption, not really that dissimilar and so I would expect to perform reasonably similar on these moderators, assuming an otherwise comparable host/mount. (most airguns are shrouded these days) I hope that reasoning makes sense to people, and to be clear I do NOT have test data to prove it, these are just my meandering thoughts on the subject.

Aesthetic nitpicking is something I'm going to do for some of these moderators, not because I believe in it, but because some people really care about these things. I personally tend to be pretty happy with form follows function, and would rather get performance over beauty, however I can also very much understand why you want your 250$ moderator to look perfectly at home on your 2500$ Daystate. To that end, I go through and nitpick finishing of both the internals and externals of some of these designs. Please don't think I'm innately this anal-retentive about these moderators, as I could largely care less, but for those who want to know, I strive to answer. If you don't like the aesthetic nitpicks, I'm actually inclined to agree with you, so just skip the first paragraph of every section.


The test protocol. The muzzle of the moderator is exactly parallel to the pickup, and separated by exactly one meter. The milspec protocol for firearm suppressors is 1.6 meters off the ground, however given the depth of the snow in Maine at the moment, I did 1.6 meters above the surface of the snow, and an indeterminate amount (several additional feet) above the ground itself. Two pickups were used, next to each other and equidistant from the moderator, and each test was five test shots. The results are an average of that, so ten datapoints. I hand select each sound profile (image) which I feel is representative of the moderator's overall performance. The host gun is an FX Crown .22 regulated to 135 bar and shooting JSB 18.13grain pellets at about 890fps for a total of 33 foot pounds. All tests were done with the shroud fully retracted, excluding the shroud-only test. The nearest solid surface in front which will reflect sound directly back is about 80 meters away, and so will not reflect sound within the capture time-frame. Note that a lot of a moderator's sound comes out through its muzzle, and so if you shoot with a reflective surface in front of you (such as shooting indoors) moderators will sound much much louder.

Each moderator comment has three sections. The first are aesthetic observations/nitpicks. Second is my SUBJECTIVE thoughts on what it sounded like. While testing I had a friend taking data, so these are blinded because I don't know what numbers are being produced. Then third is a brief discussion of what the sound meter said, and how that relates to how I feel the moderator sounds.

Stock FX Shroud (extended)
Sound – 288

Shroud.png

What can I say about the design? It looks like the stock FX, because it is. TypeII ano, and kinda goofy looking when extended in my opinion.

As far as the subjective ear goes, what can I say? It sounds relatively loud and hollow. Amusingly it isn't the most unpleasant sounding thing here. That dubious award goes to the moderator possibly from Wolf Airguns. (no branding or ID on the tube) If I were guessing, I'd guess the unknown brand moderator cuts the peak considerably as compared to just the extended shroud, however the subsequent and significant noise that moderator makes causes it to sound worse than the stock shroud. It is hard to say though because the separation of time between the two tests fuzzes your memory.

Looking at the test data, I’ve seen this before. It is loud, but drains quickly. You’ll notice I’ve added a new, longer, perspective so you can get a better idea of sound taper to ambient. This shroud is loud, but at least it quickly drains.

DonnyFL

Top to bottom: Donny FL Sumo, FX, Tanto

Top to bottom: Donny FL Sumo, FX, Tanto

So I actually had the pleasure of testing three of his cans and Tanto, an FX, and a Sumo. The amount of excitement, and dare I say hype, around this brand is impressive. Based on the offers of loans I got, at least in the US I think Donny outsells the competition by at least a factor of ten to one. Doing a little research, aside from sound attenuation, I hear a lot of complimentary things said about the quality of his machining. To be clear I'd never touched one before this test, so all these things are second hand reports from forum members. Because these moderators are all virtually identical in terms of design and construction, I'm going to do just one overview/nitpick of the design and finish.

That prefaced, I'm about to tip a sacred cow: I don't think his machine processes or finish is exceptional. The machined aluminum itself looks quite simple, and optimized for manufacture, which is fantastic particularly if it offers great sound attenuation. The minimization of parts count and assembly time, and the ability to work well with looser tolerances, are both big wins and these designs happen to have that. That said, I promised nitpicking and I intend to deliver. The little nitpicks are things like uneven depthing and radiusing on the aesthetic body slots (I assume the radiusing is done incidentally as part of the blasting process), the bores of the Tanto and FX look like straight extrusion, the ano looks like a type II to me rather than a more premium type III, the rear-caps have five faces rather than six so you can't grab it with a wrench, the tubes and ends don't align perfectly, and finally the designs themselves are very heavy (this may help with sound attenuation).

The big one that surprised me though was what I found inside the Sumo, which was major chowdering on half the length the inside of the main tube's bore. Maybe the boring bar wasn't stiff enough, or the tool head was dulling and gumming up, who knows, but either way it is pretty ugly and it is underneath the anodizing so it was clearly shipped that way. To be clear it is not visible when in use and doesn't affect the the shooting experience of the moderator in any way so this definitely still falls under the category of nitpick, but it is still there. Anyway the sum of all these things is I would say they are reasonably made, the machining and finishing are neither rave-worthy nor something I'd knock them for. And if this paragraph doesn't get some angry comments, I don't know what would. Truly no ill will is intended though, these are just my observations having a whopping total of 3 Donnys on hand to compare with the other major brands.

Cores on all three are also the same, plus or minus can diameter obviously. They are a monocore with a wrap of what appears to be stainless steel mesh held with masking tape and then a wrap of felt also held with masking tape. Simple and, if third party accounts are anything to go on, highly effective. Worth noting is that the two small cans use a black felt while the Sumo uses a tan felt.

Donny FX

DonnyFX.png

Sound – 73.2
Mass (grams) – 135.5
Volume (mm^3) – 118,941
Length (mm) – 126.5
Diameter (mm) – 34.6
Exit OD (mm) – 8.0

This thing sounded great, surprisingly great. It is quiet and “clean” sounding. It is quite heavy though, despite its small size, and you notice this in how it changes your gun's balance, handling, and POI. This additional mass could possibly help it damp sound though.

In terms of peak, it beat the mean and beat the median. That said the trace doesn’t look quite how I’d have expected, as I was expecting a cleaner peak and faster drain from such a simple design. I can see why people like these though. The big surprise upset here was that the peak was higher than the Tanto. That said I wouldn’t call it a big upset, because the difference is within margin of error.

Donny Tanto

Donny Tanto.png

Sound – 71.2
Mass (grams) – 100.0
Volume (mm^3) – 94,324
Length (mm) – 126.6
Diameter (mm) – 30.8
Exit OD (mm) – 7.2

This sounded louder than the FX, more “pop” to it, which is exactly what you'd expect. To what extent I hear that vs. I hear what I expect is unclear, thus data. Again this one is a chunky little bugger, having some real gravity to it despite being so small.

If I were a betting man, I’d say it is that smaller muzzle bore that gave this smaller design comparable performance to the FX. I stand by what I said though of it sounding a whisker louder, and some of the noise on the trace supports that. Let me put it this way, cash in hand choice between the two, I’d pay the ~25$ premium for the FX because I still think it sounds a little better.

Donny Sumo

Donny Sumo.png

Sound - 108
Mass (grams) – 187.5
Volume (mm^3) – 209,393
Length (mm) – 165.8
Diameter (mm) – 40.1
Exit OD (mm) – 8.0

This one was a big surprise. Given the performance of the Donny FX I was expecting hammer slap to be all I heard. That is not what happened, it actually sounded as loud or louder to my ear than the DonnyFX. It also lacked that “clean” sound of the FX, picking up just a hint of an odd metallic sort of sound. I'll mention this sound a couple times, as this is not the only moderator which has it, but I'm guessing it is resonance inside the moderator. My buddy and I talked a lot about what analogy best describes it. I think the best description is like a high tension steel cable failing, where you have both an air “hiss” and that metallic resonance. He thinks it sounds a bit more like a tennis racquet. Either way it is kind of a hiss-twang kind of thing, and I want to be clear there sounds like just a hint of it in this moderator.

This is a bigger upset, being a lot louder than, not just the other two Donny designs, but was actually the third loudest moderator here. You can see the peak is quite high, however the subsequent dip is quick, which is probably why it sounds much quieter than it actually is. It looks to me, on the trace, like it produces sound for a fairly long time though, not tapering to ambient even by the end of the trace, which I would expect to be the moderator resonating, which is also not exactly fantastic. It is hard to say why exactly this is worse, however both hearing it and measuring it I’m confident in the result. Just because something is unexpected doesn’t mean you can discount it.

0dB

0dB Airgun Moderator

0dB Airgun Moderator

0dB.png

Sound - 63
Mass (grams) – 145.4
Volume (mm^3) – 133,871
Length (mm) – 167.5
Diameter (mm) – 31.9
Exit OD (mm) – 9.5

If I were going to pick a moderator for most visual appeal, it'd be this one. Nice matte black finishing, some good stylistic flairs, etc. I don't think it looks particularly good on the Crown specifically, both because the diameter is too small and because the tapered rear face looks dorky unless put on a shroud or barrel with a smaller diameter, but it does seem to have some nice eye appeal. In terms of how well the caps align with the tube, I'd say this can is second only to the Huggett, however you can see some tool/work piece deflection at the tips of the aesthetic slotting particularly at the front of the can. The whole thing also appears to have been carefully and thoroughly blasted. This external beauty though is contrasted with the core, which isn't as nicely finished, and it appears to have basically the machined equivalent of hair curlers and washer baffles. Clever on the outside, but a well-worn path in terms of design on the inside. While there are clearly points for bespoke tooling to grab and unthread it, it isn't my can and I didn't want to force it or risk marring it so left it at that. In that regard you could almost consider it a Hugget clone, as the stylistic similarities both inside and out are pretty apparent.

Given the sound of the Huggett, I was expecting this to sound similar. It didn't, it sounded louder than the Huggett to me, louder than the DonnyFX too. But it sounded as quiet or quieter than many of the moderators here. My subjective ear puts this somewhere at the good end of the pack, but not the best.

This design was technically the quietest of any moderator here, beating the Donny Tanto (second best) by about 8 points. That said, the victory may be a bit hollow given that it did it by being 50% heavier, 25% longer, and with 30% greater volume. It also didn’t sound great, to my or my buddy’s ear, so the fact that it won startled both of us. Hell he was recording all the data and even he didn’t see this coming. You can see on the trace why too, because it produces a lot of noise after the peak. It just so happens that the peak is quite low. I think we’ll see this story repeated, and it isn’t an indictment of any design lowest is lowest and peak probably carries across distance better than subsequent lower noise, it is just worth noting that this is my explanation (excuse) why I didn’t see this coming despite having listened to it.

TKO

IMG_20190301_140534553.jpg
TKO.png

Sound – 81.6
Mass (grams) – 73.1
Volume (mm^3) – 88,984
Length (mm) – 167.6
Diameter (mm) – 26.0
Exit OD (mm) – 7.7

There is no branding on this moderator, and its owner didn't recall its brand, but it sure looks like a TKO from the outside. Same size, same look. While it looks like carbon fiber, I believe it is actually an aluminum tube with a faux carbon wrap on it. Ends appear to be delrin, as do the baffles. All this matches TKO to my knowledge. Fit and finish is not what you'd call great externally, and while this moderator has clearly been loved hard for a couple years, the fake carbon wrap and coarse machine marks on the delrin end I'd say put this moderator in not so great standing from an appearances perspective. It also appears to be held together by solely glue, which I discovered accidentally when giving it a gentle test to see if the end was threaded in. Oops. :( This is easily the skinniest moderator here, which I believe is done intentionally to clear iron sights. Internally the baffles appear to be a simple slightly conical design. It is small and light though, so I could imagine this being the moderator of choice for things like pistols where thin and light are what you want. In that regard it is the only thing tested here which is really suitable for the application, and I give it extra points for being so very light weight. A lot of sacrifices are worthwhile to shed weight, and this appears to make the most of them, or at least a lot of them. There is a real purity of purpose about this can's design, and I really really like that. The baffles look like a mini lathe with an auto feeder could crank them out all day long. The aluminum tube looks thin and light, and the faux carbon wrap may help dampen its vibration. Ease of assembly cuts manufacturing cost, and it doesn't get much easier than glue. Thus as a package it really really works, from a design/assembly perspective.

I'm torn regarding what to say about this little moderator. It is the smallest, lightest, and least expensive commercial design tested here. It'd have every right then to be the loudest, but it sure doesn't sound it. Far from it actually. It isn't whisper quiet, that is for sure, but I would also place it somewhere at the louder end of the middle of the pack. I guess the best thing I can say about it is that it is surprisingly not loud, all things considered.

This design had every right to be the loudest, and it just wasn’t. It does an excellent job cutting the peak, given its size, and just continues making noise afterward. I don’t know how much more could be expected from this little thing, and there was nothing else like it here to test. I’ll be curious to see how it stacks up in the length vs. attenuation comparison.

Wolf Airguns? -the big one

Possibly Wolf Airguns’ moderators? No branding on them to be found.

Possibly Wolf Airguns’ moderators? No branding on them to be found.

Wolf large.png

Sound – 89.8
Mass (grams) – 296.9
Volume (mm^3) – 325,927
Length (mm) – 253
Diameter (mm) – 40.5
Exit OD (mm) – 8.0

Again no branding here, but this looks like a Wolf Airguns K-baffle moderator of some form. To be brutally honest, this thing looks and feels and is built a lot like a .22 caliber PB silencer and I will be relieved to get it back to its owner. It is just aluminum K-baffles in a big tube. That said the quality of finishing and machining is perfectly adequate. Neither exciting nor anything to complain about. The tool paths are clearly visible on the baffles, however this uneven surface can reduce sound signature, so I wouldn't fault it there. This thing is also HEAVY. It is easily the biggest moderator here in terms of weight and length. The finish appears to be some kind of powder coat, which does a nice job of making it look good while hiding the tooling marks on the outside. The rear mating face was clearly machined post-powder-coat, presumably in order to maximize alignment precision. I'm not sure exactly how abusive to felt moderators some of the higher pressure big bores are, however if I owned such a gun which frayed felt cores, a moderator with an architecture more like this might be the ticket because it looks like it can eat just about anything an airgun can throw at it.

This was the second loudest moderator here, to my ear, and it had that metallic sound I mentioned above in spades. Not good. The weight also caused considerable POI shift.

I learned this the hard way myself, back when I started this project: firearm silencer designs make really lousy airgun moderators. Such is the case here as well. What would you expect given K-baffles with no cross jetting?

Wolf Airguns? -the smaller one

Wolf Small.png

Sound – 114.8
Mass (grams) – 179.3
Volume (mm^3) – 111,857
Length (mm) – 153.1
Diameter (mm) – 30.5
Exit OD (mm) – 6.8

Again no idea what this is, but it is full of some pretty basic aluminum conical baffles. Same F&F as the other, minus the powder coat. Everything fits nicely and looks like it has been made to a reasonable standard of quality. Worth noting here is that the exit OD may be factory, however the exit “crown” pretty clearly is not, having been badly chowdered by what looks like a handheld drill with a multi-flute countersink bit. The only noteworthy from a design perspective is that this is the smallest exit OD of any moderator sampled here, which is probably why the muzzle end has been futzed with. And still there is something I can't quite put my finger on which I really like about this moderator. For some reason its appearance and proportions and feel just seem pleasing to me. Then again I'm just some crazy guy on the internet right?

Contrasting the appearance was the sound. This thing brought to a head all the discussions regarding the “metallic sound” we're getting from some moderators. This one had it so loudly I finally put my finger on “snapping steel high tension cable” as my favorite description. It really has that metallic almost “twang” plus the whipping sound of the cable flying through the air. Other descriptions are a tennis raquet, punching metal, a sheet of steel being flexed and making that “twang” sound, and so on. It also sounded louder than the stock shroud, maybe not in peak, but certainly in terms of total sound. What can I say, this moderator is unequivocally the worst sounding one I have EVER heard.

So the peak wasn’t exactly low, but you can see clearly why I called this the worst sounding moderator of this test. Despite having a similar design to the TKO, it seems like someone sank a lot of testing into the TKO and not so much into this. The thing lights up like a tuning fork, and is the only moderator in this entire test which keeps making loads of noise well past the end of the trace. This design is just a loser, no two ways about it. Disappointing really, because I kinda liked how it looked.

Neil Clague

Two custom Neil Clague moderators. The top one was built for a .30 caliber FX Impact, the bottom one was built for a .25 caliber Marauder.

Two custom Neil Clague moderators. The top one was built for a .30 caliber FX Impact, the bottom one was built for a .25 caliber Marauder.

Talk about a name, Neil was in this game before it was cool and is still one of the most storied brands. The two moderators I have of his were made model specific, like all his designs. One was for a .25 caliber marauder, the other for a .30 caliber FX impact. These moderators have been through a couple owners, and show some signs of use. It is also worth noting that another Clague owner I've chatted with had insisted that his designs were simply empty tubes. That was a bit surprising to me, but these Clagues are clearly not empty tubes.

Clague Marauder .25

Sound - NA
Mass (grams) – 143.7
Volume (mm^3) – 150,585
Length (mm) – 189.6
Diameter (mm) – 31.8
Exit OD (mm) – 7.0

The .25 caliber Marauder moderator I actually didn't test. Why? Four reasons. One was due to the performance of the other moderator, which we'll get to. The second is what I discovered when I peeked down the core: it was full of rust. The baffles themselves look like maybe freeze plugs to me, and they're covered in rust. Third is that there is nothing here internally which appears unusual or special. By this point you're probably tired of me saying “hair curlers and washer baffles,” and in a twist there are no hair curlers. The baffles are flat with holes in them, and they appear to be spaced with what looks like a machined white plastic which I'm guessing (wildly) is PVC given its surface finish. Fourth is that the threaded end appears to utilize a male thread unique to the mrod shroud, and taking the time to fabricate said thread adapter didn't sound like the most fun I've ever had with my pants on. For now I'll pass on this one. I will say that a .25 caliber pellet (6.35mm), the intended payload of this moderator, is awfully close to its 7mm exit hole and even closer to its 6.87mm entry hole. As far as external fit and finish goes, this moderator has been quite beat up, but looks like aluminum which was painted black once upon a time. It also appears to have had hidden seams, that is to say was finished on the lathe as one piece, so from a cap-fitment perspective looks great.


Clague FX Impact .30

Big Clague.png

Sound – 152.6
Mass (grams) - 325 (maxed out precision scale, used hanging scale which is less precise)
Volume (mm^3) – 493,214
Length (mm) - 276
Diameter (mm) – 47.7
Exit OD (mm) – 9.6

The .30 cal FX Impact moderator is big, and I mean BIG. It is easily the largest here, and is the second heaviest despite its carbon tube. This is probably in part because the end caps are quite large and solid aluminum chunks. The whole thing looks like it was finished on the lathe, which creates that seamless look of the other moderator. Before it was unceremoniously drilled and then taped back up, I bet this thing had some serious presence, particularly in the sun to light up that carbon. In that regard, despite the weathering and ELU modification, it looks great. The core is, again, hair curlers and washer baffles. In this case it looks like a tan colored foam held back by cross drilled alu. cylinders. Said alu. cylinders do not appear to be deburred and look like they were drilled by hand as the spacing is uneven. The baffles look all the world like freeze plugs to me. They could just as easily be something else, but the punchline is that they are effectively flat dividers. I should note a couple things about this can, I am at least the third owner, and I do mean owner because the previous owners all were so dissatisfied with this can's performance it was given away multiple times, eventually to me. One of the previous owners, who I'm told is an airsmith of quite some repute, tried venting the carbon tube in a variety of locations to improve performance, which allegedly it didn't, and so taped it back up.

Even given the warnings of the previous owner, I was shocked by how loud this thing was. It is not quiet, and I don't mean not quiet given its volume, it is just flat out not quiet. I'm guessing this was the second or third loudest moderator here, which is quite something given its size and weight. There was an accompanying very large POI shift downward. I guess you could say I'm just not a fan here.

It was the loudest, it was the heaviest, it had the largest volume by a huge margin (well 2.6 times the average, and 30% more than the second largest), and it was the longest. While not included in the test results, I did try wrapping the outside of the tube in a sound barrier material to ensure the sealed holes weren't leaking sound, and they aren't, so this moderator kinda just has to own its performance or lack thereof. I’m staggered. Not only did this result shock me, it shook some of the very foundations of what I believed to be true regarding moderator performance. I just don’t know what else to say.

Huggett Belita

Huggett Belita airgun moderator

Huggett Belita airgun moderator

Huggett Belita.png

Sound - 75
Mass (grams) – 97.2
Volume (mm^3) – 90,648
Length (mm) – 120.1
Diameter (mm) – 31
Exit OD (mm) – 7.0

So I don't know how much these bad boys go for in the UK, however stateside I believe I'm correct in saying that they are the most expensive commercial moderators available. This tiny little Belita will set you back 170 'murican pesos. Given the prices, steeply increasing with size, I was expecting some combination of space magic and fairy dust inside this can, or at least something complex and difficult to machine anyway. You can certainly burn a lot of money doing complex surface machining on a CNC. I was surprised when I popped it open to discover felt, hair curlers, and washer baffles. Don't get me wrong, it was all very nicely machined inside and out, in terms of precision of machining I'd definitely give the Huggett the highest score of any moderator here as all parts including the caps fit and align flawlessly with the tube, but it is just flat faced discs, felt, stainless steel mesh, and alu. hair curlers. I don't mean to be crass, it is all very nicely made even where nobody is going to be looking, but it also isn't exactly unusual or unique in there. Again maybe these bad boys are more affordable over in the UK, and the machining is very nice, but at the end of the day it is an old and simple architecture with a shiny type II anodizing on the outside. I don't know, I guess I just expected more somehow? The similarity between this moderator and the 0dB also really jumped out at me. I don't know what kind of history exists between these companies, so I don't want to cast shade on anyone here, so I'll just say they appear remarkably similar. For what it is worth, I really like the form factor of this moderator, it is just nicely proportioned.

Subjectively, this moderator sounded pretty quiet, surprisingly so given its size. I'd definitely put it at the better end of the pack performance-wise. It didn't have an entirely pleasant sound though, it had that dreaded resonance I've mentioned before. It is subtle, but it is definitely there.

So I’m actually going to go out and say that I’m pleasantly surprised by how well this little bugger did. It is tiny, the shortest design here and despite its simple architecture it worked in cutting the peak quite well. That said, look at the trace; it is still resonating (or at least appears to be) quite significantly at the end of the trace. I think this is part of why this moderator just doesn’t quite sound as nice as it could and should. An updated architecture with better damping might be easy for Huggett to implement, and could make a good design even better.


So I wanted to add a bit of a break in here, because this is the phase of the exercise where I post test results of “my” designs. As I noted in the introduction, a buddy of mine helped me immensely. (he would say I stole some of his ideas, in a good natured way) If it weren't for our friendly competition over who can make the quieter design, my test results below would be CONSIDERABLY higher. Just look at my other tests from earlier. Going into this, I really had no idea how I'd stack up, and the answer is without his help and encouragement I'd have been somewhere in the middle of the pack. So a big thank you to him. Ben if you're reading this, bugger off you stole my best ideas! :P Humor aside though, I really can't thank you enough, and if it weren't for our rapid-prototyping and massive associated pile of discarded experimental cores, none of this would have happened. Having someone to bounce ideas off of, or borrow ideas from, and the ability to turn complex CAD geometries into physical objects so quickly made this possible.

Also a thanks to all the space monkeys out there who jumped on my crazy ideas and tested a core and provided me with feedback. Your collective feedback was contradictory and confusing, and your support was very much appreciated. :) You know who you are and if you have one of these early cores, I'm going to make a limited time offer: you can send it in and for the cost of return shipping I'll re-core it with this new design in 1/2-20UNF which I can say with absolute confidence is much quieter.

Top to bottom: Mus, Pilum, Levitas

Top to bottom: Mus, Pilum, Levitas

Ultimately I tested three designs. The only one with real development behind it is the small 35x120mm design. The longer design is just a lengthened version of that, basically an answer to the question “what would you do if you weren't so length constrained?” The largest design is again a scaling up and recycling of ideas from the smallest design, with a few other completely experimental twists thrown in. It answers the question of what I'd like to try now without length or diameter constraints, but like the smaller OD “long” design it simply hasn't been optimized. It is kind of an odd duck too, as I have a sneaking suspicion that, despite being the size of a big bore can, it is at least closer to optimized for small bore performance. Going in I didn't really know how all of these would measure up, but also didn't have time to tweak and optimize them, so I just kinda hoped the smallest design's principles scale, and went for it. More data, more better right? Whats the worst that could happen?

Levitas

Levitas rev.9.png
Levitas.png

Sound – 60.4
Mass (grams) – 48.1
Volume (mm^3) – 116,308
Length (mm) – 120.2
Diameter (mm) – 35.1
Exit OD (mm) – 8.4

Credit to BobO for this one, he said I couldn't just call everything a gas diode I needed a name, and now that there are three different sizes in a myriad of different flavors I do see his point. So the smallest I named Levitas, latin for lightness or fleetness of foot. It represents my core principles when approaching this project which were to keep everything as small and nimble and light weight as possible. A lot of subtle tweaking and revision brought the last (rev.4) gas diode design forward to this. The same basic principle remains of use an air stripper to first pull turbulence away from the pellet, then delay the air with a gas diode, and then damp the sound produced. The locations and proportions changed though, and in a quest for ever more volume the dual walled tube system was abandoned. Looking at the scope, it is clear the gas diodes are noisy, they make a lot of sound doing what they do, and so the relative split of sound damping to flow delaying also changed. I think this is part of why the rev.4 design sounded louder than it actually was: it produced a lower peak, but noise afterward for a longer time period. Put all together and it is a nice quiet package. There are also some tweaks to aid in assembly, which became necessary as my buddy and I ripped through core designs. Anything to speed the turnaround. :P The core itself is 3D printed, but unlike previous revisions (and the experimental cores) which used ABS, this was done in 20% high modulus carbon fiber reinforced nylon. Why? Better strength, better solvent resistance, and quite frankly because it just looks sexier. I had special stainless steel thread inserts I'd been using with the ABS 1/2-20UNF core designs, because the ABS really needed the reinforcement, but the carbon nylon just doesn't need them, and yanking that shaves 6% off the mass right there. As far as the skeletal section on the end, just like with previous designs, those struts and trusses are there to hold sound damping material. It doesn't really show up in CAD, so you'll have to take my word for it that it is there. You could say it is my take on hair curlers and washer baffles. :P

I'm not sure I'm a good critique of my own fit and finish, because I obviously made all the design decisions and also know exactly how it was done, but I'll give it a go. Externally the carbon tube looks like a carbon tube that has been post-machined so it isn't ribbed for her pleasure like some of the carbon products you see out there in the airgun world, and has been clear-coated to protect the carbon. (that ribbing is the result of the mandrel wrapping, part of the manufacturing process) The silvered engraving is nice, but isn't perfect; tooling marks are visible in it if you look closely. Ends have an unusual look and texture, and are completely basic being flat and square without embellishment. Cap alignment with the tube is adequate but not exceptional. It all has a machined finish. Disassembly holes (for disassembly tools) are on the rear face only and have been functionally, but not aesthetically, deburred. There is also a visible seam on the rear face between the rear cap and the core. Unlike externally, where everything is machined-finish, internally print lines are clearly visible. It is hard to see what exactly is going on inside by looking down the tube, but it sort of appears to have four closely spaced baffles at one end, and then a ladder-like structure through the rest of the can. The bore path itself looks clean though, which it should because it was reamed to final dimension once the whole can had been assembled. I'm not sure if this critique is fair, but I hope it is a good description at least.

As far as how I think it sounds, I'm obviously biased so you shouldn't listen to a word I say. That said, I think it sounds very quiet, particularly for its size and weight. Nice tone, no resonance. Kind of a puff followed by a quiet hiss of the air draining. Of all the moderators tested today, I'd guess this is among the quieter designs. With your head down on the rifle's comb, hammer slap is definitely the predominant sound, and the reg filling is very noticeable too.

The trace looks pretty good to me here. The peak has been effectively blunted and, unlike in previous gas diode designs, I’ve incorporated enough sound damping that the noise from the diode isn’t overwhelming. It steadily and in a reasonable time frame tapers to background. I think some of this is also changing materials with non-homogeneous mass distribution and which are innately damped, so even if made in the form of a literal tuning fork, they won’t resonate.

Pilum

Pilum.png

Sound – 51.8
Mass (grams) – 62.9
Volume (mm^3) – 161,883
Length (mm) – 167.3
Diameter (mm) – 35.1
Exit OD (mm) – 8.4

I nicknamed this design Pilum, after the long skinny javelin the Romans used to such great effect. So I had a choice when designing this: one gas diode or two. If I were running a ballsier and more powerful gun, 100 foot pounds or so, I think two would have been the better choice. As it stands though the peak is effectively blunted in my design by just one, and in the super short Levitas, so I used the extra space for more sound damping. I wanted that sound profile to drop off as quickly from the peak as possible in this form factor. I guess you guys are the judges of whether or not that was effective.

Design and finish are identical to the Levitas, minus the engraving. Again this design is the same, just more.

Sound wise maybe this sounded a little better than the Levitas? Hard to say really, and I wonder if I'm not just fooling myself because I'm expecting it to be better. The “puff” sounded about the same, but maybe a little less sound from the moderator draining pressure after? Because I know this design so intimately I really feel like I’m fooling myself thinking it is quieter, and it just might not be. If it is quieter, it certainly isn’t a night and day difference. Hammer slap and the reg filling are the predominant sounds either way.

Looking at the Pilum and Levitas traces back to back, it is clear the primary advantage is in sound damping not in peak. Yeah okay sure whatever, the average peak was about ten points lower, but it should have been more. The quicker taper to background is nice though. This design might have benefited from a little less sound damping in exchange for another gas diode module. Or maybe just a sound divider somewhere down in the damping. As I learned competing against Ben, with moderators the devil really is in the details, and while this design is better than the Levitas it isn’t “enough” better given its increased length, mass, and volume. I took a guess at the length scaling and got it wrong, essentially. Further tuning and refinement will be required, I’m just not satisfied this design is living up to its potential capabilities.

Mus

Mus.png

Sound – 103.6
Mass (grams) – 111.0
Volume (mm^3) – 321,428
Length (mm) – 162.4
Diameter (mm) – 50.2
Exit OD (mm) – 8.4

I named this design Mus, latin for “mouse,” half as a joke because this was meant as my go-for-broke HUGE design and half because I was sincerely hoping that, at this size, the thing would be absolute mouse-fart quiet. And for those who shoot indoors, there is a big difference between an outdoor mouse fart and an indoor mouse fart. I was hoping for the latter. Also I have a confession: I'm a Cheaty McCheaterface with the mass on this one. Why? I didn't have any carbon tube in this size on hand, so I 3D printed the tube and core from ABS. This makes it lighter than a proper carbon fiber tube and carbon fiber reinforced nylon core, but more delicate as the core design relies on the stronger carbon nylon and a 1mm walled ABS tube isn't going to win any awards for durability either. Basically it is fine for testing in this configuration, as it can easily hold the pressures, but ignore the mass number because it isn't representative of anything you'd actually want on the end of your airgun under normal circumstances unless perhaps you were a strictly benchrest shooter. This is a weird design in that, as I said before, is big-bore sized but is probably much more optimal for small bore airguns. The real changes here, aside from scaling everything up, are in the sound damping area. I have some crazy theories about sound penetration and variable density foam, and just kind of ran with them. I have no idea if they made things better or worse.

As far as fit and finish goes, this design is BY FAR the worst moderator seen here. Cap to tube alignment isn't even a metric, as it isn't even pretending to have it. The cap color is white while the tube is gray, which hideously clashes, and the whole thing has an air of delicacy without any poise or sophistication. Flashing is clearly visible everywhere, as are the uncleaned remains of supports. The choice of white also means every single smudge of dirt or lead or grease or whatever clearly shows up on the surface, and can't easily be cleaned. Basically it looks like a hastily made and very ugly prototype, which funny enough is exactly what it is.

To my subjective ear, this actually a fair bit louder than the Pilum and Levitas, at least in terms of the initial peak or “puff.” The subsequent pressure draining sound was quieter. I'm pretty disappointed. I was hoping for the mechanical action to be the only audible sound or at least for it to be much quieter, but it definitely wasn't. I guess this is what happens if you're a goof like me and think that these things should just scale. Oh well. :/

Talk about eating humble pie, that peak was nothing short of a disaster. Clearly the gas diode didn’t even pretend to scale, and so did a downright abysmal job of stomping down that peak. Clearly more development is necessary, although I’m vaguely curious how this would perform on a big bore. I don’t have any evidence for it, however I have the sneaking suspicion that the air output from a shrouded .22 caliber Crown just isn’t great enough to saturate the diode and make it work. Thus it behaves like oddly shaped conical baffles, rather than as a diode. This may not be the case if considerably more air were put through it, and it is the only poorly performing big design tested here which has a plausible mechanic which could make it actually quieter if put on a more powerful host. The sound damping also clearly worked, however it is unclear if it did that due to sheer volume or if the variable density foam actually helped.



Discussion

So that is a lot of information I just threw at you, and a lot of lines to scroll through to compare all these different moderators. Let me start with a convenient chart which puts all the important data together in one place.

Moderator Performance Summary Chart

So lets talk about this quickly before moving on, and just point out some general trends. Most obvious, I put the highest and lowest values for every category in bold. This makes it pretty stark that the Clague was the clear loser in this test, it was the worst for all four categories. Largest and smallest volume, to be fair, aren’t necessarily a “best” and “worst” category, but while being smallest is arguably an excuse for being loudest largest would be reason to be quietest or at least among the quietest. A few other honorable mentions to make here, the Huggett Belita was the shortest by just a whisker, and was below the median peak sound, which I think is a solid accomplishment. I’d give Huggett a round of applause for that one, because again the Huggett and TKO have every excuse to be the loudest designs here and they just aren’t.

Lets move to some data visualizations that’ll make trends and comparisons easier though shall we?

Sound vs. Length Graph of Moderator Performance (trend line not statistically generated)

So maybe this will ring a bit ironic to some people, as I’ve bucked the bullpup trend in my preference for the Crown, however I’m more opposed to moderator length and mass than I am to moderator diameter (volume). So in an effort to visualize this, and compare longer and shorter designs on a level playing field, I generated the above chart. Please note the the trend line was not statistically generated. That is a fancy way to say I eyeballed it to show the trend I’m trying to highlight, while excluding all the noise in the data in the top right hand side of the chart. The short version is that the “ultimate” moderator would be in the bottom left hand corner of the chart, producing 0dB (punny, I know) with zero added length to the rifle.

Realistically what we see is a good cluster of the Hugget, smaller Donnys, and 0dB. From this metric, you’d say they’re all good competitors for each other as they’re in about the same performance class. Now you could tilt that line to make the 0dB and Pilum look relatively worse and the Belita look better, but honestly I’d say there isn’t really enough data here in a cluster to really fit a solid trend line. So it is just a guess either way. I confess, I’m very happy with the Levitas here, as this chart clearly shows it is doing what I wanted which is being short and quiet.

Sound vs. Mass Graph of Moderator Performance (trend line not statistically generated)

As I said above, length and mass are my two big things I look at when I want to build a moderator. And it is a real prickly pear because sound damps mass, and length makes it easier to make a moderator quieter. Again the hypothetical optimal here is to be in the bottom left hand corner, zero mass and no sound, and the more bottom-lefty-ish your design the better. Again I inserted a general non-statistically generated trend line to try and highlight the performance of “the pack.” I don’t want to kick the Clague here every time, so I’ll say it once and be done: in almost every chart, the Clague is going to be off in the bad corner. Now lets move on.

So the pack, as I’m referring to them, here show the trend I expected. More mass, more quieter. :P The TKO finally found itself in the game here too, as this metric doesn’t penalize its small diameter as necessarily harshly. My opinion is that this is the most important chart shown here, because it clearly clusters the good commercial designs along an axis where users can make decisions between sound attenuation and “size.” It is worth noting that the Sumo is in this unexpected never never land, way off the performance curve. I’ve said it before, and I’ll say it again, I think the Sumo is optimized for eating the air from more powerful guns. That said, I genuinely don’t know if this test were performed on a more powerful rifle it’d be on the curve. It might well be. It might also not be, it is very possible that its sound attenuation vs. mass will still leave it an outlier. Without data I just don’t know.

I’m tooting my own horn here, to put it mildly, but again this chart is showing me pulling off PRECISELY what I aimed to do, which is make moderators stupidly light weight and reasonably quiet. The Pilum and Levitas broke the trend, but on the good side of the line and by a significant margin. The Mus not so much, that is off in the “what was I thinking” rhubarb. I’ve given all my excuses before, so no need to revisit them, but I do have an idea for twin nested gas diodes, basically a gas diode inside a gas diode, so such a large design could saturate at least one diode irrespective of power output.

Sound vs. Volume Graph of Moderator Performance (trend line not statistically generated)

Ask people about airgun moderator design and you’ll invariably get a bunch of people telling you that the primary factor is expansion volume, and design architecture is secondary. Hell I even believed it. Clearly not though. Again better designs are toward the lower left hand corner. The non-statistically-generated trend line here was the one I am actually most uncertain about. It could easily change slope, making the Pilum and 0dB look better or worse. More data would be better.

Before everyone jumps on me urinating on the sacred monument of airgun moderator faith, which is to say expansion volume, let me be clear that not only is there a trend, there are potentially two trends here. The obvious trend line I placed at the bottom clearly shows performance improvement with volume. Lets then address the elephant in the room: why did ALL the big designs do badly? Well you could almost fit another trend line up there around the Wolf, Sumo, and Mus. If it weren’t for the Mus, you could make the claim that the cluster represents volume without good sound damping.

The Levitas is, once again, clearly doing what I want it to be doing, which is to say clearly below the pack for sound attenuation vs. volume. Where I’m less happy is the Pilum, which I alluded to in its section god knows how many paragraphs above. Looking at the Levitas alone, I was certain it wasn’t performing up to its potential, and now this chart shows that in start contrast. If you draw a line between the Levitas and Pilum, the slope will be considerably steeper than that of the pack’s. Thus it doesn’t appear to be operating at its potential. Yeah, sure, I didn’t optimize it I just winged it, but that is just an excuse.

Mass vs. Length of Airgun Moderators

So this chart is a little silly, because obviously diameters can vary wildly thus any correlation between mass and length would be loose at best. Note the two trend lines, for one I locked the intercept to the origin, and the other I did not. Amusingly the former has a higher Rsquared, and you might say “makes more sense” because a zero length moderator you’d expect to have zero mass. On the flip side of that coin though, at zero length, you’d still expect to have the mass of the mount and cap though no? The second trend line suggests that these features have negative mass, because a zero mass design should have a hypothetical length of 98mm. WE HAVE SUCCESSFULLY DISCOVERED ANTIMATER!

Mass vs. Volume of Airgun Moderators

This is the less silly version of the former chart, the plot of mass vs. volume. It is important to note why there are two trend lines here as well: moderators are essentially cylinders, so their volume should increase exponentially with their surface area. You can judge for yourself here though. In this case more optimized designs are above the curve, you’re looking to be in the top left hand corner where you have great volume and no mass.

Notable standouts here are the Clague .25 and .30s, the Sumo, and the TKO. I’m just thrilled I finally have something positive I can say about the Clague .30, which is that its volume to mass ratio appears to be ahead of the trend. There isn’t much out there in right field to compare it with, but a win is a win and that is a good thing. Also surprising to me was the Sumo, which really feels like a brick in the hand and on the gun, but by this it seems to be either hanging with or slightly ahead of the pack.

So remember when, on the Mus, I said I was a Cheaty McCheaterface? Well you would think this is the chart that clearly shows that, that it is curve-breakingly light for its volume. But it appears that I was wrong. While writing this, and staring at the chart, I noticed that the Pilum, Levitas, and Mus all line up. So I scratched an eyeballed trend-line on the chart, and this was the result. Given that the relationship shouldn’t be linear, this suggests the Mus might not even be ahead of the curve, it might be on it or even behind due to increased core mass. Hard to say. It gives me some hope though that I might be able to build something in this size class which has about the same mass as a DonnyFX or 0dB.

Future avenues of inquiry which most interest me are twofold: first I have a great interest in eccentric bore designs. While an integral moderator core upgrade for the Edgun Leshiy would be a very fun project and catches my eye, in general the ability to sling most of a moderator’s volume out of the scope path offers advantages and allows much larger moderator volumes without detriment. Second I’m very interested in moderator development on more powerful rifles. While an integrally shrouded .22 at around 30 foot pounds (or considerably less) is probably the largest use case scenario for a moderator (guessing) and is exclusively what I shoot (minus Baikal target pistol), these slug guns and big bores have started catching my eye. Something suited for the 100+ foot pound range that isn’t absolutely enormous and is very quiet would also be a very interesting and fun challenge. In both cases I don’t own the gun, and it is somewhat ridiculous to purchase a gun just to play around designing a moderator for it, but it isn’t out of the realm of possibility. I am just some deranged guy on the internet after all right?

The big test is coming.......

Silent Thunder Ordnance

IMG_20190227_164809656E.jpg

To my knowledge, there has never been a large scale comparative test of moderators like this before, where every design is put on the same exact host and tested on the same meter on the same day. We’re going to do it with a proper meter capable of capturing peak volume as well as generate a sound capture, to provide a more complete look at the moderator’s sound profile, dominant frequency, and so on.

Going from left to right, back to front, we have Wolf Air?, Neil Clague, Neil Clague, 0dB, TKO?, STO experimental, STO experimental, DonnyFL Sumo, Wolf Air?, DonnyFL Tanto, DonnyFL FX, STO Levitas, and Huggett Belita.

The big test is coming soon, watch this space……..

Product Change - Scalpeldashi

Silent Thunder Ordnance

20% carbon fiber reinforced nylon scalpeldashi sheath, seen here next to a figured bubinga scalpeldashi

20% carbon fiber reinforced nylon scalpeldashi sheath, seen here next to a figured bubinga scalpeldashi

Earth shattering news here: all scalpeldashi now come with a sheath. That little announcement just changed your life right? These new included sheaths are 20% carbon fiber reinforced nylon which is durable, cut-resistant, and has an attractive textured finish. The only exceptions to this are the one-offs which are sold with a matched/paired sheath, those do not include a second CFRN sheath.

Airgun Moderator Design, Performance, and Development (part 4)

Silent Thunder Ordnance

FX Crown with Levitas, an ultra light and compact 1/2-20UNF moderator

FX Crown with Levitas, an ultra light and compact 1/2-20UNF moderator

And now for the latest installation in the thrilling adventures of airgun moderator design. You can find part three here. In this episode I test the culmination of quite a lot of designing and testing and tweaking to create an effective 1/2-20 UNF “universal” moderator which I’ve named Levitas, latin for lightness or fleetness of foot. A fitting name for a moderator which is a mere 120mm in length, 35mm in diameter, and 65 grams in weight, but has the sound attenuation of a much heavier and greater volume design. This series started off as a pet project, but I’ve gotten so much interest in moderator design and so many requests for a 1/2 UNF version I decided to build one. So after much time, effort, and refinement, here it is.

Levitas, a 120x35mm 65 gram 1/2UNF moderator.

Levitas, a 120x35mm 65 gram 1/2UNF moderator.

Adapting the original concepts to a 1/2UNF universal application is more challenging than it sounds. The FX Crown's unique design, and unique associated moderator, was more than just a gas diode. The large thread allowed for significant flow to be tapped off from around the bore. Were size no constraint a blast chamber integral to the moderator could be used to fulfill the same function, however this is volumetrically inefficient when it comes to this level of sound attenuation. Further, the lack of a flow-through system along the perimeter will put additional load on the gas diodes as there is no alternate pressure relief, they simply have to eat it. This leads to one final concern, which is air stripping. Without the expectation of some sort of muzzle brake on the rifle to pull turbulent gas off the pellet near the muzzle, the moderator must now possess this as well.


An image of the rev.4 core design clearly showing the three distinct stages. Not shown are the rubber and foam elements which attach to the skeletal structure seen toward the muzzle end of the moderator.

An image of the rev.4 core design clearly showing the three distinct stages. Not shown are the rubber and foam elements which attach to the skeletal structure seen toward the muzzle end of the moderator.

So, how to go about it? Well in this case I went with a three stage system. The first stage is, of course, the aforementioned blast baffle/air stripper. A symmetrical conical baffle designed to bear the brunt of the blast out of the airgun's muzzle, and cleanly strip that turbulent air off the pellet to maximize accuracy. Following that, the second stage, are two of a new and more efficient gas diode which stops or at least delays forward air flow. Unlike the rev.1 and rev.2 gas diodes, which were comparatively volumetrically wasteful, these waste much less of the precious internal space. They also offer cavernous flow-chambers, reflexing vastly more air. All in all, they are a massive design improvement, and I really couldn't be more pleased with them. The third stage is something incorporated all the way back in the rev.2 gas diodes, sound damping. Why should flow and sound in a moderator be the same from end to end? It wouldn't, not if the moderator is working properly anyway, so it stands to reason the design of the moderator itself should change from end to end to match this. Most moderators out there seem to either focus on flow disruption or sound damping, but my approach of first flow stopping then multi-layer sound damping appears to be more effective than either flow stopping or sound damping alone. The CAD images don't capture this sound damping structure well, showing just the skeleton around which is it installed, however it is built of high surface area foam, a new type of foam I’ve never before featured, and rubber. Again this is a combination of materials arrived at after much testing of different combinations and designs.

Before we get to the test results, I also want to bring up something I’ve touched on before, which is peak sound vs. total sound. It is difficult to relate and difficult to quantify, this concept of total sound, because in essence you’re trying to put a number of a squishy human perception. I’ve done a series of experiments with RMS (root mean square), however so far these have not yielded good consistent data. You see there is more to a moderator than just the brief “uncorking” sound produced when the pellet exits and the maximum pressure wave gets out, there is also the sound of your moderator draining that pressure slowly over time. A bare muzzle may have a very high peak, but the subsequent drop back down to zero will be very rapid. Meanwhile a moderator design which effectively slows the flow of air out may have a very quiet peak however because the moderator spends a long time, relatively speaking, draining out all that air until it equalizes with ambient pressure, it may produce more total sound. How this relates to human perception of loudness is more complicated still, because both intensity and duration of sound will affect perception. At longer ranges though it seems the peak is what is most audible, and most likely to alert a prey animal or nosy neighbor. Thus quantifying this is next to impossible, which is why we associate a representative sound readout with each data sample. Below you can see an example in high tech MS-Paint, with the peak (what I measure) circled in purple, while the subsequent sound profile bracketed in teal.

High tech MS-Paint drawing showing what we measure, the peak, outlined in purple as well as a significant but thus far difficult to quantify sound profile bracketed in teal.

High tech MS-Paint drawing showing what we measure, the peak, outlined in purple as well as a significant but thus far difficult to quantify sound profile bracketed in teal.


So enough foreplay, how about test results? I used the same protocol as always, with the moderator separated from the pickup by 1 meter, perpendicular to the muzzle. Excluding the Crown Shroud test, which was done with the shroud extended, all tests were done with the Crown shroud collapsed. I also pulled the old foam filled moderator out to once again provide fair comparison against a “typical” foam/felt filled moderator (your hair curlers and washer baffles) design of equivalent material, design, volume, etc.



Shroud Extended - 214.4

Shroud Extended - 214.4

Shroud Extended - 214.4

Been there, done that. It is loud. It is the baseline, it is what it is. I always insist on repeating the baselines because some days, some atmospheric conditions, god knows some moon phase just results in different numbers. So I always strive to meter the baseline/s so that the later data has good context.

Rev.1 Gas Diode – 122.6

Rev.1 Gas Diode – 122.6

Rev.1 Gas Diode – 122.6

Again, another baseline. The rev.2 is a major design improvement, but it is always good to see progress. Here we can also see one of the things which I strove to improve upon, which is the quantity of noise produced AFTER the peak.

Foam Filled Moderator – 172.4

Foam Filled Moderator – 172.4

Foam Filled Moderator – 172.4

Again, this is an open cell foam filled moderator, intended to be a test analogue for the common high surface area moderators out there which use felt or foam. Here we see a phenomenon I alluded to before, all the way back in the first tests. The sound just tapers faster on these sound damping, rather than flow-stopping, designs. So you get higher peak sounds, the moderator is definitively louder, however it empties that air more quickly and more quietly. We can see that in the image, the initial spike is quite high, but the subsequent taper is more rapid. One has to wonder if part of the reason why felt/foam baffle-less moderator designs are so popular because of this phenomenon: while they may technically be louder, particularly at close range some people may perceive them as quieter. Borrowing or purchasing a popular and highly regarded commercial moderator design, such as a Donny FL, might be a good idea both to get a better understanding of what sound profiles they produce but also to provide a baseline for comparison that other people can relate to.

Rev.2 Gas Diode – 115.3

Rev.2 Gas Diode – 115.3

Rev.2 Gas Diode – 115.3

Still doing comparisons and baselines, what can I say? The second lowest peak, and one of quietest total sound profiles of all the moderator designs tested today. Why? Well this moderator you'll recall is a combination of gas diodes and sound damping in the center, and with off-axis flow-through around the perimeter, again with sound damping toward the muzzle end. The result is a design which slows the initial blast, and effectively and quickly drains the pressure and quiets the resultant sound. Thus there is both a fairly mute peak, and good quick tapering of the remainder of the sound profile.

Levitas (Rev.4 Gas Diode) (1/2-20UNF attachment) – 81.2

Levitas (Rev.4 Gas Diode) (1/2-20UNF attachment) – 81.2

Levitas (Rev.4 Gas Diode) (1/2-20UNF attachment) – 81.2

So this is the culmination of all this testing, the moderator which this is all about. More efficient gas diodes and a sound damping system work together to bring the peak down to the lowest moderator yet tested. And I don't mean just in this round of tests, I mean of all time; this is the quietest airgun shot I’ve ever sampled. I was surprised and pleased, to say the least. Remember this moderator maintains the same overall length, 120mm, as the other designs which ALL were direct thread into the Crown shroud. Integrating a 1/2UNF thread mount means you now have to eat up precious length and volume inside the moderator for the threads, so I would have been exceptionally happy if it were able to simply match the rev.2 gas diode, beating it by a significant margin was an unexpected but pleasant surprise. You'll notice though that the peak is not much higher than the rest of the sound profile. Both of the previous gas diode designs (revs.1&2) had pickups around the perimeter, out of the bore axis, which tapped off gases from inside the Crown Shroud and likewise vented them out of line with the bore. This is more useful than you might think, as it allows you to place dampers directly between the sound source and the exit for at least some of the air. This isn't possible with a 1/2UNF mount, for obvious reasons. While such a design could hypothetically be integrated into the blast chamber, with the loss of volume and effective length it just wasn't feasible thus was omitted. Even still though, it is great performance by any standard, so I'm very happy with it.

What will the next advancement be? Not sure yet, but as long as people find this interesting we’ll keep experimenting. I do want to test other moderators. A dirty secret of the firearm suppressor industry is that values can vary significantly from day to day due to ambient conditions, and my testing shows this is no different with airgun moderators. That said the values are reasonably close enough as to provide a very general basis of comparison, which would be very nice to have. So if anyone has a moderator they would be willing to loan for testing, if it has a 1/2UNF thread I’d be happy to give it whirl. Watch this space!

Comments? Questions? Fire away.

FX Crown with Levitas, an ultra light and compact 1/2-20UNF moderator

FX Crown with Levitas, an ultra light and compact 1/2-20UNF moderator

Project - Arca Swiss to Swivel Stud adapter

Silent Thunder Ordnance

Arca Swiss rail adapter for FX Crown

Arca Swiss rail adapter for FX Crown

This was a quick little pet project to make moderator sound testing more convenient and accuracy testing easier when there is a couple feet of snow on the ground. It is pretty much what it says on the tin, using the sling swivel stud on an FX Crown and adapting that to an Arca Swiss rail interface. This example is entirely 3D printed, but for a 3.5x20mm brass pin which goes through the swivel stud. The clamping force from the tripod head holds everything together. A small window provides access to the front gauge…… assuming the clamp doesn’t obscure it.

This whole thing can be machined or 3D printed, and we’re offering up the 3D digital files if anyone wants/has use of them.

Why Arca Swiss, and why swivel stud? The Harris type bipods attach via a swivel stud, and are very light weight and durable. It is also lower-profile and less marring to use a swivel stud than a rail. Regarding Arca Swiss, they’re the manufacturer of arguably the best monoball tripod head, and in so doing set the standard for mounting clamps. Now most tripod heads use them. Manufacturers in the precision rifle industry are starting to pick up on this, and you’re seeing Arca rails more and more often on chassis systems. Oddly though, it seems a lot less common in the airgun industry.

Project - FX Crown Moderator (part 3)

Silent Thunder Ordnance

FX Crown with carbon fiber gas diode moderator

FX Crown with carbon fiber gas diode moderator

You can find part 2 here. This is the third installment of our attempts to make a novel and effective moderator for the FX Crown, the basis of which is a linear Tesla Gas Diode. The ideal is to generate an extremely compact, light weight, and POI-shift free with exceptional sound attenuation for its size. As an aside, we’ve received a lot of interest about our FX projects. The moderators in particularly have gotten quite some attention. If you have additional questions, please feel free to use the contact form in the top right hand corner of our website to get in touch.

It has been about two months since the last major update, and in that time we’ve gone through a couple different designs, tests, and revisions. Here we finally bring it all together and do one comprehensive analysis of all these evolutions. But first a question:

Why do many if not most moderators have the same architecture from end to end? It didn’t make sense to us either. This concept of flow-stopping at the rear and sound absorbers at the front is really the evolutionary theme with this test, because we have discovered it is very effective. It is more effective than either purely sound absorbing materials or baffles alone. Gas diodes revs.2, and 3 as well as LIM, use this to great effect. You first blunt the air flow with the baffles, and then you mop up the sound with the damping materials, in a manner of speaking anyway. Simple right? Regarding what materials we used, we did a bunch of experiments (not published) on all sorts of things, including several grades of the very popular felt. Ultimately specialty foam and rubber won out across the board, and so that is what was used in all subsequent tests.

Sound analysis

Same standard protocol and data capture/averaging as in the second test, although we switched pellets to JSB 18.13gn for this test. I do want to note quickly that atmospheric conditions, minute variations in the setup, pellet choice, and about a dozen other things will affect readings, which is why we retest our baselines EVERY SINGLE TIME. It is also why these numbers completely don’t line up with previous test numbers, as we wouldn’t expect them to and weren’t trying to make them. Conditions were about 31 degrees Fahrenheit, sunny, and with a light breeze.

FX Crown with shroud extended.

FX Crown with shroud extended.

Stock Shroud Extended - 199.6

About what you’d expect here, obviously the loudest test. You can once again see the sound bouncing forward and backward in the tube as well. We’ve seen this all before.


The OG gas diode from our first test. Exceptional sound attenuation for its size and weight.

The OG gas diode from our first test. Exceptional sound attenuation for its size and weight.

Tesla Gas Diode rev.1 - 138.2

This is our OG gas diode from the first test, the silver one for those paying close attention. As before, it extends the time frame where noise is observed, as well as blunting the initial peak. Not much else to say that hasn’t been said before. I don’t have a hypothesis about what that small initial positive peak is, it seems too close to the uncorking event to be the hammer slapping the valve, however I’d guess they are some other mechanical function of the gun. Either way, in this sample, it is very visible thus noted here.

An image of the core of our rev.1 flow-through gas diode

An image of the core of our rev.1 flow-through gas diode


Tesla gas diode rev.2, amazingly it is even quieter and lighter than rev.1

Tesla gas diode rev.2, amazingly it is even quieter and lighter than rev.1

Tesla Gas Diode rev.2 - 112.0

The original gas diode had exceptional performance for its size and weight. What if you could cut that weight down by an additional 11% though, bringing it down to just 57 grams, all while attenuating sound even further? That is the concept which brought forward rev.2. It is still flow through, and still uses linear Tesla gas diodes at the rear, but after the diodes blunt the forward movement of the air, we applied sound attenuating materials so the subsequent draining of pressure out the muzzle end was even quieter. And it clearly worked. Beyond just lowering the peak output, it reduced the post-peak sound in both volume and duration. For people using cheap sound meters which can’t capture the peak, or cell-phone apps, this is probably what they’re measuring anyway. Regarding the core design, it is difficult to effectively show as it is a multi-part assembly which isn’t conducive to cross-sectioning in CAD. In brief though, at the rear, are the same flow-through structures on the outside and gas diodes in the core. Beyond that is a skeletal structure onto which the foam and rubber are installed. The same flow-through vortex cap as rev.1 is used at the muzzle end.

Rev.2 gas diode moderator. Not seen is the foam and rubber which populates the skeletal section at left, and further mutes the report.

Rev.2 gas diode moderator. Not seen is the foam and rubber which populates the skeletal section at left, and further mutes the report.


Rev. 3 gas diode

Rev. 3 gas diode

Tesla Gas Diode rev.3 - 100.6

Like rev.2, this design uses gas diodes at the rear and a foam and rubber damper at the front. The major changes though are larger diodes, so no flow-through and a solid cap, along with a more aggressive rubber and foam section. It is a great design, but there are a few tweaks it could benefit from in regards to the damping section. We’ll get to the why of that in the next section, but suffice to say its minor improvement in sound attenuation is likely both caused and offset by some issues with the damper section. There is good reason to pursue this design further though, because the lack of flow-through means it could be redesigned for use on guns other than the crown, something we’ve gotten a lot of requests for. It is also worth noting that scale is a challenge with the rev.1 and rev.2 gas diodes, they are about as small as is possible without a major equipment reconfiguration. Omitting the exterior flow-through section has allowed these diodes to grow, which has other potential benefits.

Rev.3 gas diode. Not seen, but which would be to the right, is the foam and rubber assembly which acts after the gas diodes. This design uses a different cap (not pictured) as it is not flow-through.

Rev.3 gas diode. Not seen, but which would be to the right, is the foam and rubber assembly which acts after the gas diodes. This design uses a different cap (not pictured) as it is not flow-through.


LIM moderator sound profile

LIM moderator sound profile

LIM - 91.2

LIM stands for Less Is More, the concept being maximum usable volume and a minimalistic design. It uses the same post-baffle dampers (not pictured) as the rev.3 gas diode. And I mean quite literally the exact same, we just swapped that section of the moderator for testing. The image below is actually outdated, as the baffle design has since been tweaked, however for now this design is a dead end. Why? Well moderator design is a balance between silence and accuracy-disrupting turbulence. In this case in its less-turbulent guise it was louder, and still caused accuracy issues, and in this test format it creates even more significant accuracy disruption but is a bit quieter. And that is really all there is to say about it.

LIM moderator core. This uses the same damper assembly and cap as the rev.3 gas diode. Unfortunately this design appears to be a dead end, as it induces accuracy issues.

LIM moderator core. This uses the same damper assembly and cap as the rev.3 gas diode. Unfortunately this design appears to be a dead end, as it induces accuracy issues.


If you’ll forgive the hasty scrawl, here is a quick target to confirm whether or not a design has accuracy issues. Note that LIM shows only 4 rounds, as it threw a flier so bad it was entirely off the paper.

If you’ll forgive the hasty scrawl, here is a quick target to confirm whether or not a design has accuracy issues. Note that LIM shows only 4 rounds, as it threw a flier so bad it was entirely off the paper.

Accuracy Analysis

Knowing that moderators, particularly overzealous ones, have a nasty habit of messing with accuracy, it is important to shoot some quick groups to ensure everything is working as it should. These groups were shot standing off a tripod which, if you’ve never done it, is more stable than hand holding but less stable than prone with a bipod. The range was 59 yards, the temperature was 31 degrees Fahrenheit, and there was a gentle breeze moving both the pellets and the target itself. Groups are all 5 rounds. It is worth noting that some of the shots tear the paper, and they have a tendency to tear it downward, but this is not keyholing I can assure you. Sighters were taken on another sheet, not shown here.

The rev.1 gas diode has already been extensively shot, so no need to revisit that here. So I started with the stock shroud as a baseline, which produced an extreme CTC distance of .67”.

The rev.2 diode did well, as expected, no notable POI shift and it was just a whisker over 1MOA here at .63” CTC. Omit the one high round, and it shrinks to .49”CTC. Certainly no accuracy issues here, and this design has been tested a bit before and should have no issue.

The rev.3 gas diode didn’t do as well, at .85” CTC, however this was almost certainly due, not to the diodes, but to too aggressive a foam and rubber damper section. The same issue reared its ugly head with the LIM which actually managed to suck some of the foam into the flight path, have it be trimmed by the pellet, and spit it out producing a flier which was off the paper. The less disruptive rev.3 diode didn’t send a pellet that wild, but clearly the damper section needs to be scaled back. This will cut sound attenuation to some extent, but will cure the accuracy issues.

LIM is just straight out. One round was off so far it missed the entire paper. Beyond that, the 1.07” CTC was less than inspiring, as was the POI shift. It serves as a great demo though regarding how a moderator can be made significantly quieter at the expense of accuracy.

And that is it for part 3. If this series continues to attract interest there will likely be a part 4. Let us know what you’re curious to see.

FX Crown with carbon fiber gas diode moderator

FX Crown with carbon fiber gas diode moderator

Project - FX Crown Magazine; Fixing The Fliers

Silent Thunder Ordnance

FX Crown magazine, 3D printed, in .22 caliber. The name of the game is to create clearance for the pellet skirts so that there is a lower propensity for fliers than with the stock magazine.

FX Crown magazine, 3D printed, in .22 caliber. The name of the game is to create clearance for the pellet skirts so that there is a lower propensity for fliers than with the stock magazine.

It seems we’ve got a bit of a theme going here with FX Crown projects. People seem to like them though, so we’ll keep going.

The problem de jour is the magazines. We’ve already touched on this with our FX Crown Single Shot Tray post. The long and short of it though is, at least with the Crown, if you use a single shot tray you’ll notice a lot fewer fliers and your groups will tighten up. Why? Obviously something about the magazine is damaging the pellets.

My hypothesis is that the damage is being done to the skirts. There are three reasons for this. First is obvious, the skirt is the most delicate part of the pellet. The second is that the skirts on JSB pellets is actually significantly larger diameter than the pellet head. This is done, presumably, to maximize gas seal. But, and here comes number three, FX magazines are designed and machined essentially in 2.5D, that is to say straight and square vertical walls. This means they are easy and fast for FX to manufacture on a 3 axis CNC milling machine, but it also means that as the magazine snickity-snacks from one index to the next, the pellets are being shoved around and stopped, not on their more robust heads, but on their delicate skirts. Obviously that isn’t a win.

First off, credit where it is due to rj2239 for being the inspiration for this project. I initially sank my teeth into this hearing the MISTAKEN assertion on the forums that a Crown magazine is just a mirrored Impact magazine. Let me dispel this myth now, they’re not. They are very very similar, but are not the same in just a few critical tolerances. This stands in contrast to the FX Dreamline which FX claims will use an identical magazine to the FX Crown. Hopefully then this project can benefit FX Dreamline buyers as well. Regardless, even though I only used rj2239’s follower (and may still redesign that), the half dozen clever little fixes and small parts links were all invaluable to getting this done. So kudos and thank you.

So what did I change? Well the concept is quite simple: if the skirts are wider than the heads, provide clearance in the magazine for the skirts. This way the pellets are pushed around by their heads not their skirts. Aside from building the mag to Crown dimensions rather than Impact dimensions, the other minor change I made was to the support structure for the alignment slot. I’m not sure what printing technology, or clean-up methodology, rj2239 was using, however when printing his designs I essentially gave up cleaning that out by hand and started cutting the slots with a mill. Most people don’t have access to those sorts of tools, so a simple rethink of the supports in that area so it could be easily cleaned up with a fine knife such as a Scalpeldashi. (shameless plug, but it is what I used. I carry one for a reason.)

So by this point you’re asking how to get your hands on one of these magazines. We’re giving away the design files for free, so they can easily be 3D printed. Figure they’re worth what you paid for them, all humor intended. For those so inclined who want a transparent face cover, and don’t have access to a laser cutter, we’ll also sell you the raw cut acrylic face plates.

How to go about converting all this into a magazine, and what do you need?

Tools you’ll need at bare minimum:
3D Printer
Metric Hex Keys
Scalpel (or equivalent small sharp blade)
File
Needle Nose Pliers
Superglue

You would additionally benefit from/ideally own:
Quality ABS filament (as opposed to PLA)
Acrylic Face Plate (transparent)
Drill Press
Drill Index
Acetone
Hacksaw
Threadlocker
Squeeze clamp

Parts (all links go to Amazon for convenience, however they can be sourced anywhere):
M1.5x3 O-ring (3mmID, 1.5mmWD)
M3x5 Brass Insert
M3x3 Grub Screw
M3x10 Countersink Screw
2mm Brass Rod
Spring (from retractable badge)


Step one: print the parts. If you’re going to use one of our clear acrylic covers, you only need to print the magazine body and magazine follower. If you aren’t, you’ll want to do the face plate as well, perhaps in something transparently/translucent. It is a free country and all, but I would recommend you double check your printer’s calibration first and use a fairly fine layer height.


Step two: clean up everything. Clean up the alignment slot on the bottom of the magazine body (I use a Scalpeldashi for this with a #11 blade), and clean up all the edges. Also, if you have a round file of the right diameter, it can be invaluable in cleaning up the magazine follower.


Step three: dry-fit. Dry fit the magazine body and face plate in the gun to make sure in step two you cleaned up that alignment slot correctly so that the bolt-probe clears and your overall thickness is good.


Step four: acetone. SEPARATELY dip the magazine body, follower, and if printed the face plate in acetone. (don’t dip an acrylic face plate, seriously) Allow them 24 hours to cure before moving to the next step.


Step five: drill critical tolerances. If you don’t have a drill index, you’ll want to fudge this step using whatever tools you have available, a scalpel blade being the most likely candidate. The following parts should be bored to the following dimensions:
Follower - 29/64” (will vary, in some cases significantly, based on material and print settings)
Magazine center through hole - #31 drill bit
Magazine center to shoulder (blind, for brass insert) - #4 drill bit
Magazine corner (grub screw) - #39 drill bit


Step six: assembly and final dry-fit. Dry fit everything together excluding the spring. Install the brass bushing by pressing it through from the back. Insert the grub screw in the corner, and thread it in. (this can be done backwards to make it faster/easier) Cut off a little brass rod piece and and glue it in the hole in the face plate. Glue an o-ring in the blind hole in the face plate. Place an o-ring in the center pillar of the magazine so it generates friction between the magazine body and face plate when the two rotate relative to each other. Test that the follower rotates freely, add a drop of pure silicone oil or wax if desired. Check manually for pellet and probe clearance, feed, and function under no spring load.


Step seven: install the mainspring. Break open one of the ID badges and remove the spring. If the ends aren’t correctly bent to install in the magazine, bend/cut them now. I personally find it easier to install the magazine body end of the spring first, then coil it around the central pillar and use a squeeze clamp as a “third hand” to hold the spring while installing the follower end. Needle nose pliers are invaluable here. Remember this spring will act much like a constant force spring, so getting the absolute maximum possible number of coils around there won’t significantly increase spring pressure. Apply a drop of pure silicone oil to the spring, and test for function.


Step eight: Assemble the magazine fully and test one last time.


Step nine: Add a hind of threadlocker to the center screw, tension the face-plate as desired, and allow to cure for 24 hours.

And you’re done. Enjoy! I shoot this magazine personally, so the design may be updated from time to time as I make improvements.










Project - Dope Card Holder

Silent Thunder Ordnance

FX Crown with an 11mm dovetail DOPE card.

FX Crown with an 11mm dovetail DOPE card.

So when we hunt with airguns, there are four common threads:

Night vision image of another local night predator.

Night vision image of another local night predator.

  • We hunt around a series of targets/stations from a known position

  • Targets are pre-ranged, and often pre-shot, so that the hold is known

  • Often this is done at night, when re-ranging/shooting a target to test hold is inconvenient at best

  • We’re forgetful and with half a dozen targets, you’re always double-checking your DOPE sheet to make sure you have the right hold for the right target

A DOPE card holder designed to attach to 11mm dovetail is the obvious solution. A few additional design requirements/caveats were that we wanted something easy on-easy off with just one tool, we wanted a flex mount to handle recoil and getting banged/caught on things, we wanted a card backer which could be exchanged to different sizes but also directly written on, and we wanted a non-destructive break-away feature so that when you inevitably catch it on something hard it doesn’t cause any damage to the rifle or itself.

Prototype 11mm dovetail DOPE card.

Prototype 11mm dovetail DOPE card.

The original design, seen at left, was a bit chunky and long, adding unnecessary length to the whole system.

The final version is slightly more clever, cutting the length significantly, and made up of just seven components. It slips easily on and off a dovetail rail with just a slotted screwdriver or coin, the center is a piece of flex tubing which bends to absorb recoil and can be pulled off if hit/caught on something. The card backer itself is 1/8” thick, and while black is pictured, transparent is also easy. Clipping a notecard to the backer using a binder-clip, the more common strategy, is also easy as this thickness works well with the small binder clips.

We may update this concept over time. One possible avenue is to replace the card backer with a sheet of a glow-in-the-dark material, such as moonglow, to make it readable in pitch black conditions. Tritium illumination is also a distinct possibility.

FX Crown with 11mm dovetail DOPE card.

FX Crown with 11mm dovetail DOPE card.