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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


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.


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


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.

Donny Emperor

DonnyFL Emperor as tested on an FX Crown .22. Of note is that this model was bored for .22, not .30

DonnyFL Emperor as tested on an FX Crown .22. Of note is that this model was bored for .22, not .30

Sound – 81.0
Mass (grams) – 436.6
Volume (mm^3) – 536,804
Length (mm) – 266
Diameter (mm) – 50.69
Exit OD (mm) – 8.55


The first thing that jumped out at me about this wasn't the size, it was the weight. In fact it was so heavy, I had to pull the core out and weigh it in parts as it was maxing out my scale. For those who don't speak metric, that is a whisker shy of a pound. It also is the only thing I've yet tested which is heavier than the Clague, and although it has a larger bounding volume it is a little shorter. Internally this, and the Ronin, differ from the other Donnys I've handled in that, instead of three chambers of varying sizes and two baffles, these have multiple chambers of identical size and far more of them. The Emperor also now has wire mesh around the outside of the felt as well, and it is held closed with zip-ties rather than the usual black masking tape. There also appears to now be not-insubstantial space between the outside of the core-wrap and the tube, effectively creating a permeable barrier between the inner core and an outer chamber of sorts. It may seem like a small detail, but this could have a substantial impact on ultimate performance, causing these designs to perform much better than their diameter would suggest. Fit and finish is otherwise identical to the other Donnys, as described above.

Before I leap into testing, I want to note that this Emperor was marketed and sold for .22/.25, but Donny said these came out a little on the snug side for .25 so really it is best as a .22 can. This is probably because, with a couple stacked tolerances and such a long mod to amplify any tolerance issues, you want that size exit hole to quite large to reliably clear a .22 pellet. The point I'm trying to get at though is that this was very much NOT made for .30.

My initial reaction to this design was surprise, and in a good way. Given all my testing with large diameter designs, I was expecting this to be much much louder than it actually sounded. Maybe it sounded a bit like a Huggett Belita but without the ring of the Huggett? What I'm getting at is, if you didn't know it was an enormous moderator, you'd never guess it by listening to it. It didn't seem to have that sound of very high peak and low subsequent sound you (or rather I) expect from a large diameter can. Another thing I want to note here is that the muzzle is substantially farther from the shooter's ear than with other designs, and the face is much wider, so it is possible some sound attenuation to the shooters ear occurs based simply on the form factor. Put another way, this can moves the “muzzle” of your gun almost a foot further away from your ear than no moderator, and then casts a significant shadow. Given that your muzzle may have only been two feet away from your ear to start with, this is likely not inconsequential.

So how did it actually do? Not bad really. Again I was expecting armageddon, something up in the Clague range of mid hundreds. To be below 100 was great, in fact this design was almost as good as normal sized moderators. Looking at the traces, there is clearly less residual sound than many other smaller designs, but it isn't dead silent either. It is enough that, if you were to measure with an unsuitable sound meter or a phone, you might get erroneous numbers suggesting it is quieter than say a 0dB. Given this design's length and weight I can't exactly call this result great, being almost as good as a design a quarter its mass, but it sure is a heck of a lot better than I'd have guessed.

Donny Ronin

DonnyFL Ronin as tested on an FX Crown .22

DonnyFL Ronin as tested on an FX Crown .22

Sound – 103.6
Mass (grams) – 267.7
Volume (mm^3) – 325,562
Length (mm) – 160.5
Diameter (mm) – 50.82
Exit OD (mm) – 8.11


I covered above, on the Emperor, the internal and aesthetic observations of these two. Beyond that, they are largely similar to the other Donny designs I've tested from an aesthetic perspective and are covered in greater detail above.

I also want to note that this design was sold for .22/.25, not .30. I too would expect this exit OD to be too tight for .30.

My subjective impression on how this design sounded was “peaky,” that is to say producing a peak which is much higher than you'd expect given its draining sound. That isn't to say it sounded quiet, because it really didn't, but having passed my initial surprise given the performance of the Emperor I guess this sounded neither luxuriously quiet nor ostentatiously loud. It definitely has the kind of sound delivery which would make it hard for an untrained ear to judge how loud it actually is, if that makes any kind of sense. I do worry I've listened to too many moderators at this point, and so my subjective impressions are starting to diverge substantially form what a lay-person would perceive, however this is why hard data exists.

Well, for those who say this sounded quieter than the Sumo, I believe them because it is..... barely. We're probably within margin of error here, but on a previous day the Sumo averaged 108 and the Ronin averaged 103.6. Of course both of these are substantially louder than smaller diameter designs, but there it is. I suspect, although could easily be wrong as I have been so many times before, the design alterations of the Ronin will give it a further edge over the Sumo on higher flow guns.

As a small aside to these two Donny tests, I expect someone will point out that, while these designs may have been bored for small-calibers, they were intended for higher power air handling. To this end I screwed them to my Crown .30 (80 foot pounds) and ran some dry-fire shots through them. The results were erratic, but far from flattering, producing the highest peak of the session at 220. I wouldn't read into that though, because I also ran a couple other designs dry for the purposes of comparison and discovered that dryfires cause moderators to behave very strangely. In short, a dryfire test of a given moderator may or may not be representative of its performance with projectile, and you'll have no way of knowing until you test it properly. :/


0dB Airgun Moderator

0dB Airgun Moderator


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.



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.

Trident Ramus

Trident moderator by Ramus Technology

Trident moderator by Ramus Technology

Sound trace for the Trident by Ramus Technology. Notice that ~7kHz wave which is part of the peak.

Sound trace for the Trident by Ramus Technology. Notice that ~7kHz wave which is part of the peak.

Sound – 92.6
Mass (grams) – 113.1
Volume (mm^3) – 158,814
Length (mm) – 160
Diameter (mm) – 35.55
Exit OD (mm) – 6.87

THIS MODERATOR WAS TESTED ON 4.15.19, SEPARATE FROM THE REST OF THE MODERATORS TESTED HERE. I did test a number of other designs which were tested on this day, and they were all within a few points of where they were before, however in the interest of full disclosure I wanted to put this in.

So I know, when I initially did this writeup, that I thought the 0dB was most visually appealing. I FULLY rescind that, this is without a shadow of a doubt my favorite production moderator from an aesthetic standpoint. The the aesthetic slots cut up to the edges of the ports end perfectly consistently. You can just barely make out where the ball-nose endmill cut its path around the little indents at the muzzle end of the tube, that and some of the faintest lines where the exterior of the tube was turned down to size are the only machine marks, and they are tiny. Cap alignment appears as good as the Hugget. And, also importantly, there are 6 of those body flats on the main tube, so if necessary it could be gripped by a soft-jawed vice or wrench for loosening/tightening the front cap. The sheen is a little higher than anything else seen in this test, if I were guessing it'd say it may have been bead blasted or media tumbled rather than sandblasted like Donny's. (note, I don't have a citation, but I recall reading somewhere that Donny sandblasts prior to ano and I have no reason to disbelieve it, but without citation such a claim should be viewed skeptically) Internally I do have one more nitpick: the core is .51mm shorter than its alloted space in the tube. Essentially the core is 3D printed, not via FDM, but by the looks of it via a 3D Systems MultiJet printer. I suspect this is how the price is kept so modest despite a very intricate design would would be very challenging to machine. This core is then wrapped in felt. The tolerance discrepancy is totally aesthetic, as the aforementioned felt keeps it from rattling around. This core is what then makes up the muzzle exit OD specification, as the aluminum tube merely is a pressure vessel and has the attachment threading for your rifle. It is a very clever design, all in all. I'd also add that, out of all the commercial moderators tested, if I were walking, cash in hand to buy one, it'd probably be this one. The two big selling points for me are the innovative core design and the light weight. The fact that it looks cool is just a bonus.

For the subjective ear I'd say it sounds higher frequency than the typical hair-curlers and washer baffles designs. It is slight, but is noticeable. I don't know if this will show up on the trace, or I'll look like a fool, but there it is. I'm guessing the air handlers toward the distal end which swirl the air are the cause for this. It also sounds a little “puffy” if that makes sense, like the event is slightly more sustained. I'm not sure if that is why it sounds slightly louder, the frequency and duration, or if it is because it peaks louder.

Well there it is, a peak of 92.6. I was genuinely surprised it was that high. Given how it sounded to my ear, I wasn't expecting it to meter like a mouse-fart, but I wasn't expecting it to be quite that high either. Looking at the trace, I'm genuinely not quite sure what to make of it. The ramp-down after the peak is quite interesting, as initially (for ~1ms) it is a VERY clean ~7kHz. And it is like that on all the traces. It also, to my subjective eye, seems unusually symmetric, as if the moderator really is converting half a sound wave into a full sound wave and then propagating it. I genuinely have no idea what to make of it.

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 (under development)

Levitas rev.9.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 (under development)


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 (under development)


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.


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 UPDATED 6.13.19

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?