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You can find part 1 here. This is the second installment of trying to make a novel and effective moderator for the FX Crown based around the concept of a linear Tesla Gas Diode.
Having successfully designed and built one, I also built several other designs of various industry standards to compare it against. Those are the common felt/foam from the airgun industry and the clipped conical baffle design common to the suppressor industry (with flow-through around the outside). All that remained was to test them and compare.
So measurement-wise, I went with the suppressor industry standard which is 1.6 meters off the ground, and muzzle 1 meter from the mic. This is done with two tripods, one holding the pickups the other justifying the muzzle of the gun. This assures things are the same every time. Consistency is close to godliness, and if your data is a mess good luck getting anything useful from it. The gun is my FX Crown .22 shooting Crossman Premier HPs, and while I didn't chrono the Crossmans it spits JSB 18.13s at 874fps with +/-3FPS on average. Each configuration was fired 5 times. Six configurations total were tested and they are as follows:
Copper Gas Diode (copper references color, not material)
Silver Gas Diode
Clipped Conical Flow-Through
Here is what a typical sound data sampling looks like:
Aside from having exceptional sampling resolution, 250MSa/s that is to say 250000000 samples per second making it able to sample very very brief sound occurrence, it also can provide other interpreted data such as the most prevalent frequency, the overall length and shape of the event, etc. It is very handy, particularly when developing moderators rather than just comparing them. As you can see each sample has a LOT of data in it, multiple channels, the full spicy chalupa. The result is that, rather than a typical sound meter which is sampling one event one time, each value I present below represents multiple simultaneous samplings of each event (a shot), that event is then repeated (five times per configuration, five shots), and it all is recorded. The result is that there is an immense amount of data generated here, and then has to be post-processed, which is all ultimately distilled down into a single average of the multiple samplings of multiple events. Because my calibration is well out of date, rather than then converting to decibels which would be wrong, I just left them as unit-less numbers. This is perfectly fine for the purposes of this comparison, since I doubt anyone else is running a Bruel & Kjaer to produce assuredly accurate numbers anyway. I realize it is all a bit complicated, but hopefully the single value makes it easy and simple. Side note, these aren't powder burners, so there is no first round pop, and because regs are imperfect on the first shot after storage the gun was cycled to “warm it up” prior to testing.
Less handy were the two el-cheapo meters I had running. I've seen a lot of people taking measurements on airguns and posting it on youtube with these inexpensive meters. When last I did this it was with firearms, and years ago, so I thought maybe just MAYBE newer meters had the resolution and range to measure airguns. Several reviews on the new meter I picked up even said that it "worked great on airguns," one even claimed it compared favorably to an "expensive German meter" on airguns. While I can't speak for every meter out there, having done the testing I can now confidently say that this is not the case on this meter at least, and that while the meter will pop SOME number in response to every shot, and they're remarkably consistent, whatever it is reading isn't the muzzle report. How do I know this? Because every single configuration was within margin of error of each other. That meter claimed every configuration was about 97db average. EVERY. SINGLE. ONE. I don't know what it was reading, but it sure wasn't the muzzle. *shrug*
Shroud Collapsed - 728
Pretty much what you'd expect here, or rather if you own a Crown, exactly what you've come to know and love. That predictable loud bark. This is easily the loudest test in this series. And it is quite messy, again as you'd expect, because there really is no damping or anything of the sort. Presumably that pressure wave can ricochet up and down the shroud as many times as it wants puffing out the muzzle bit by bit. I'm guessing, just guessing, that the brake and shroud cap act as one in the collapsed position, so there really is nothing here just a reflective tube at both ends. It is possible that by modifying the action end of the shroud stop some significant gains could be seen here, so it isn't just a big sounding tube. Dampers like this could be designed for dual effect, to both eat barrel vibration (improve accuracy) and sound. This might be worth exploring, along with perhaps venting the rear of the Crown shroud...... or alternately replacing the stock shroud entirely with a lighter weight carbon fiber one that is an integral part of the entire sound dampening and accurizing strategy.
Shroud Extended - 312
Again what you'd expect. It is considerably quieter than the shroud collapsed both because of greater muzzle-forward volume, and it tapers more rapidly because the brake now can act as a choke point between the two chambers as the pressure wave bounces forward and backward. Notice the secondary spike in there. A little napkin math correlates this with the speed of sound traveling the length of the shroud. Cool stuff huh? It is possible, given a longer sampling time, we'd have seen more descending spikes tapering off.
Clipped Conical Flow-Through - 346
So this was kind of a flow-through outer shell take on the suppressor industry standard of the clipped conical baffle. The clipping diverts flow laterally, making it quieter than your typical symmetrical conical baffle, however it comes with POI shift as I discovered..... in fact over 4 MILs of “repeatable” POI shift. There were two problems with this though, the first that is in pellets this kind of POI shift is destabilizing so it'll cost you some accuracy (unacceptable), and second the crown's shroud is free rotating so any repeatability is also thrown out the window. Hence I didn't do a second pure clipped conical design, because whats the point? Speaking of whats the point, after looking at the numbers you'd have to ask whats the point of this design? It is quieter than the shroud extended, but not by a lot. Given that it is physically the longest design tested by a few milimeters, and has the most baffles, I think we can pass on this conical baffle design for further exploration. It is easy to machine though, so I can see why it is popular.
Foam Fill - 204
Now things are getting interesting. This is my attempt at good performance analogue for the all-too-common foam/felt hair curlers and washer baffles design. It is a relatively thin layer of foam constrained toward the outer surface of the suppressor and exposes maximum surface area, more than the Weilrauch's design. The muzzle end uses the same cap design as all the others, and the threaded rear uses the same flow-through design. To the ear, both my friend and I agreed this design could be the quietest of all six tests. It is hard to tell with these things, so we both were eager to see the numbers, but we both bet that this would win.... somewhat to my chagrin. Looking at the pressure wave, it is very obvious how it peaks very strongly and cleanly initially, and tapers off very quickly. This could be thought of as the visual equivalent of a clean sound moderator, pop and done. We'll get back to this, it becomes important later.
Cu - 192
Ag - 194
I combined these, as they're identical designs in essentially identical materials. (just differing color) In essence, they should be the same, and testing bore that out. It is always nice though when something pans out, in this case repeatable manufacturing being repeatable and performing consistently. By now you've seen that the numbers are lower, so the moderator is in fact quieter! All my crazy scheming worked. Why then did we both think the foamie was quieter? Remember when I said the human ear is really bad at judging sound pressure level? Well that certainly has something to do with it, your ear just can't tell what is louder than what very effectively, in much the same way your eye can't easily judge how heavy a cow is but a scale can do it accurately all day every day. There is another element I think is at play here though. The foamie had a higher initial spike, with no complex architecture to retard it, however once that passed through it tapered rapidly. The gas diode conversely shows that it is doing EXACTLY what it is supposed to be doing: extending the length of the event by holding that pressure and releasing it slowly. This means it produces sound for longer, which is a good way to fool an ear into thinking something is louder. A hammer hitting a nail doesn't sound that loud, but make something that loud continuous and you'll find it deafening. While that is an extreme example, it illustrates the point quite nicely how something which is quieter but lasts a little longer can sound about the same or even slightly louder than something which is technically louder than it is.
So there it is, in its full spicy glory. As with everything in life and science, the answer only raises more questions, more avenues of inquiry. But for now I've accomplished what I set out to do, and to my pleasure and surprise the countless hours of designing and testing and revising all built on a harebrained idea borrowed from the eccentric genius Nikola Tesla from a century and a half ago.
The title pretty much covers it. Two of our Weaver slingshots in polished copper. One is deliberately smoother, while the other intentionally shows off details like the contour lines.
After our last epic saga of airgun moderator design, this one should be a quick hit: a single shot tray for the FX Crown. Retained by an O-ring (just like the factory mags), this is the very common angled-ramp design but with a twist. That twist is rails in the profile of the pellet, in this case a JSB 18.13 grain .22 caliber, to ensure pellet alignment as it rolls down the ramp. Simple and effective.
Thanks to a legal ruling, airgun moderators are legal in the United States. This is probably why essentially all airguns now come with one. For most users though, the stock moderator is insufficient to achieve the level of suppression they desire. This was the case with my FX Crown. Strap in, this is going to be a long one. Not sure if you want to suffer through so many lines of crawling ants? Read the conclusion (final paragraph) first, and then decide if you want to know more about the journey that lead to the destination.
In another life, I did design work on firearm suppressors. Experience tells me they are deceptively simple devices; the devil really is in the details. And this runs the gamut from effects on accuracy, size constraints, sound attenuation, and tone. Given huge suppressor volume, it is relatively easy to build something quiet, so the most significant trick is making a quiet design small. The second trick though is accuracy, many extremely quiet designs cause some level of projectile destabilization and associated inaccuracy. Making a complete package which is desirable and effective is just the sort of fun challenge I’m all about.
Enter the FX Crown. Great gun, but even with the shroud extended it has quite a bark (and looks goofy). Airgun moderators have several distinct advantages and disadvantages over firearm ones. The most notable disadvantage is that the projectiles are lighter, have lower sectional density, are more subject to turbulence, and all this makes them easier to destabilize. That is the hard part. The easy part is that the exhaust gasses are cool and the total system pressure and volume at the muzzle are relatively low. This opens up a LOT more materials and manufacturing technologies. It also means moderators can be much lighter weight. The Final major advantage is the legality of airgun moderators, making complete units, parts, etc all much easier to handle.
The FX Crown has a somewhat unusual design which provides its own challenges and opportunities. For those unaware, there is a muzzle brake attached to the end of the barrel, and any moderator must be screwed not to this but to the shroud which surrounds it. This means you already have your blast baffle taken care of, as well as an existant pressure reservoir to deal with. It so means your thread will be the unique M27x1.5, not exactly an every day size. An idea I’d long kicked around but never tested was that of the Tesla Gas Diode. A diode is essentially something which allows free movement in one direction, and resists movement in the other. A common use everyone is likely familiar with is the LED or Light Emitting Diode, which is a one-way valve for electrons that produces light as a side effect. While the original design was for fluid only, and didn’t need anything to pass down the bore, in theory it could be readily adapted to be radially symmetric and have a straight bore large enough to pass a projectile. The concept simply splits and reflexes gas back on itself to create resistance which scales, the harder you blow the more it resists. Thus the idea is to restrict the forward flow of gas from the muzzle of the airgun, while allowing it to freely travel rearward back toward the barrel.
There is a second element to my design hypothesis here though. Suppressors are all stuck at a general performance class based on size, as that size is the total volume; no matter how efficient your suppressor is, you can only eat as much gas as your can’s volume….. or can you? OSS has popularized this concept recently, although Brugger and Thomet to my knowledge is its originator, predating OSS by well over a decade. The latter doesn’t really publicize their work in the United States or really much at all to my knowledge, and while the former does their designs (to put it bluntly) are way too large, heavy, and loud to be relevant or even demonstrate the forward-vented-volume concept. Their marketing is not centered around sound attenuation, but minimizing backpressure in automatic weapon actions, and to put it politely I believe them. There are a few other users of non-fixed-volume designs in airguns. Air Arms has, at least for the last few years, cut vents into their actions where the shroud meets. These create quite the startling blast to your spotter or anyone else next to you. Huggett also has moderators with mesh screens and vents over the blast area, although their cores are simply a felt/foam/whatever material over a rigid structure to protect it, very similar to DonnyFL designs.
So I wanted an unlimited volume design, something which will continuously vent gas to increase its efficiency. It is comparatively easy to disrupt a pressure wave if you can physically obstruct it. So to take some pressure, pun intended, off the linear gas diodes I wanted to create an outer chamber inside the suppressor which would allow relatively free flow of gas, while breaking up the pressure front, to allow a small moderator to ingest a lot of flow with minimal sound. Because of the size of the threading, we actually have room to pick up this gas at the very rear of the moderator, essentially tapping it off after the blast baffle courtesy of FX. This is the second half of the concept, once gas pressure has equalized in a given section it will vent more effectively rearward toward the gun, which will will then be taken up by the outer flow tubes and pass through the outer suppressor chamber. This outer chamber requires no in-line flow, so can effectively disrupt the sound. The outer chamber itself is sealed by the tube, in this case a carbon fiber tube. Mating surfaces at the rear and cap are toroidal, which automatically produces alignment with the ends of the carbon tube. This leads nicely to the muzzle cap.
Cap design is its own entire area of study. While they seem simple, a cap can have a significant affect on the propagation of sound out of the loud end. Typically disruptors and channels on the surface are desirable, to redirect sound forward and to break up any wave fronts which emerge, however for the purposes of this initial testing I wanted to use a simple cap design which wouldn’t advantage or disadvantage a particular design, and also minimized overall length. Furthermore, caps being readily exchanged, I can swap this trivially later.
For the flow-through designs the cap is quite simple. Threaded at the end, it screws to the front of the core creating a semi-seal. Outside that there are six holes of equal size and spacing to FX’s original shroud cap, so whatever tool was used to remove that can be used to install this. These are through-holes so as to provide further breathing for the outer chamber, although that is a secondary function. The outer line of holes are oval in aperture, but have an offset path. De-torquing of airgun moderators from firing cycles isn’t an issue, however this will serve to generate torque assuring everything remains tight. It will also act as one final disruption of the air as it exits. Simple to implement, and potentially advantageous. The rear face that mates with the carbon tube is, as mentioned previously, is toroidal as this naturally produces good contact and alignment.
Put simply, the concept here is that the central core aerodynamically restricts flow to muffle the initial blast while the outer core allows flow as freely as possible while disrupting the pressure front responsible for the sound…… at least in theory, in practice things can be somewhat different.
Here is the pickle: theory is where you understand things, but nothing works. Practice is where some things work, but you don’t understand why. I have a habit of combining theory and practice, where nothing works and I have no idea why. A hallmark of good science is a control, in essence a way to know if your hypothesis is valid or not. Instead of simply one control though, for optimum scienticiousness, I want three. I’ll then call up another buddy from STO to dig out the old impulse sound meter, an exotic device unlike conventional sound meters in that it measures peaks from short pressure waves rather than continuous sound, and test all four configurations. Speaking of which, all four configurations are as follows:
1) Very common in the firearms industry at the moment, even among some of the best brands, is the clipped conical baffle. This design has some, but not excessive, cross-jetting to disrupt forward flow. This design is also widely applied to both supersonic and subsonic suppressor designs, making it arguably applicable here. You might at this point be wondering why I’m not opting for the all too common traditional K-baffle, which is very effective in dealing with subsonic flow moderation. The answer is that the simple K-baffle isn’t that effective at sound moderation, comparatively speaking, although it is very easy to machine which explains part of its prevalence. The more complex and efficient K-baffles are very quiet, but induce a lot of cross-jetting which significantly negatively affect accuracy. They also tend to have tonal issues, so while the results are quiet on the meter they’re also shrill and unpleasant. Some companies, notably Dead Air Armament, have overcome this with much testing and design work but for obvious reasons I’d rather not have to extensively optimize an experimental control, because doing so would rather negate its value as a control as well as detract from the central experiment.
2) What if the clipped conical baffle works better than a Tesla Gas Diode at inhibiting forward flow in a suppressor, but is disadvantaged because it is shoved in a fixed-volume design? A scaled down clipped conical baffle stack used as the center core on the same outer core as the gas diode design would be a worthwhile control.
3) When everyone is doing one thing, and you’re doing something else, maybe that is because you’re a genius but more likely it is because you’re an idiot. I’d be foolish not to make a comparably sized design and pack it with an open-cell material like felt or foam which has worked so well for Huggett and DonnyFL. The architecture is trivial to design, so may as well run with it.
4) And, of course, the entree: my Tesla Gas Diode design. I have no doubt it’ll work, but whether or not it’ll work better than the other designs I have no idea.
And that is where things stand for now. There is a lot of time, design work, and testing between here and there. Also this blog post has dragged on long enough. So I’ll wrap it up here. In part two we’ll dive more into the gritty end of prototyping, a few more subtle elements of design, etc. Then in part 3 we’ll finally get to testing, results, and revisions.
Like I tell the wife: you want a quickie or the full two minutes? Well this, is that. I recently picked up an FX Airguns Crown, arguably the most accurate airgun. Unfortunately, with the factory moderator, it still has a bit of a bark to it. Step one in remedying this is is getting the muzzle cap off, which put up a fight, hence off to CAD to bang out a non-marring tool and….. SHAZAM! Cap is off. Should anyone else be wondering, the FX crown’s stock shroud is m27x1.5RH.
Where to from here? The simplest would be a couple nice clipped K-baffles to slip into the existing shroud when extended. A better solution though would be a bespoke moderator to take advantage of FX’s unique design. Watch this space, this project is just getting started.
The Baikal IZH-46M, I would argue one of the greatest airguns of all time. Why? Three reasons really: it is exceptionally good at what it does (shooting accurately), it is extremely convenient to shoot (no air cylinders to run out, or accessories to grab, just the gun and tin of pellets and you’re good to go), and it was very very modestly priced (about 500$ in its day). No surprise then it was an extremely popular airgun. Unfortunately, for reasons I’m not entirely sure of, they’re no longer readily available at least in the United States. If I were to guess, I’d say this was caused by some combination of the Russia embargo and Kalashnikov Concern’s financial turmoil. Either way, whole guns and spare parts have been rather hard to come by.
Despite my glowing praise for the gun, there is at least one minor shortfall: the breech can be “closed” such that the gun will discharge but not properly latched. Making this relatively minor oversight will result in popping out both breech gaskets, one of which will remain sitting on the bottom face of the breech if you’re lucky while the other will be injected into low earth orbit never to be seen again. (note on the IZH technical diagram this is part #19 and is labeled “packing ring” which is an accurate description) Thus did I fall into this trap inadvertently, and find myself in need of AT MINIMUM one breech seal. Of course two is one and one is none, so really half a dozen or so would be ideal with a way to acquire a potentially unlimited quantity.
Here is the pickle though: while some clever engineering could have made this breech use standard O-rings, the 46 uses what so far as I can tell is a proprietary tapered gasket. Like most things engineered by Russians, it is a stuperb solution to the problem, possessing elements of extreme mechanical cleverness and a bizarre divergence from GMP.
So here I am, with one gasket and looking for an easy way to duplicate it. Whipping up a nice high-resolution silicone mould based off the one positive I luckily still had seemed the obvious choice, and so I prepped a container and the gasket. Unfortunately, as I discovered, the manufacturer most likely used a high sulfur urethane to make the gasket. This sulfur poisoned the platinum catalyst, and so the silicone failed to cure all around the o-ring. This was an abject failure.
I didn’t have much hope for this, but on a lark I modeled up a 9 cavity mould, printed it out, and figured if it failed at least it didn’t take that much time. Silicone was generously poured to fill, and left to cure.
I remember distinctly looking at this sad little pile of silicone thinking that there was absolutely no way it could possibly have worked…….
…..but sometimes life surprises you for the better. It is always better to be lucky than skilled, but when you’re struck with both in one moment, savour it as it is a rare beauty. Not only did it work, it worked fantastically well producing 9 perfect little gaskets.
A moment’s work with a Scalpeldashi (I always carry one for a reason) to pop one off and clean up the edges a smidge, and we’re in business.
SUCCESS! The fit was perfect and the seal was exceptional. Velocity, performance, and accuracy have all been fully restored, and now, at least for this part, there is a hypothetically limitless supply so I can go about losing them as fast as I care to. This begs the question: what other “irreplaceable” airgun seals might I someday blow which now I can replace? Time will tell.
The SIG SAUER MPX, a very popular gun at the moment. There has, for somewhat baffling reasons to be honest, been a resurgence in the popularity of pistol caliber carbines. I personally had thought this trend had died in the 90s’ with the proliferation of rifle caliber platforms in comparable sizes. But for some reason, they’re back. Shooting the MPX, owned by a friend of the company, I can see why too: it can be shot at pistol-caliber-only ranges, it is reasonably accurate, it is cheap to shoot, it is essentially devoid of recoil, and it is fun.
A friend of the company recently visited with his MPX. Moving from a ban state to a free state, he has a surplus of neutered 10 round magazines, otherwise identical to their full capacity brethren, but limited by a follower block which is an integral part of the magazine floor plate insert. At 50$ per magazine, almost highway robbery for a plastic magazine if you ask me, his ban-state collection is worth the value of a whole new firearm.
SIG glues their baseplates on ban-state magazines, but a few firm taps with a mallet or a little judicious application of a heat gun will readily break them loose and allow them to slide off. You can then remove the magazine floor plate insert w/ restrictor. But how to hold the magazine baseplate on then? You could simply cut off the restrictor, however if you wanted to go backwards you’d then be stuck.
3D printing to the rescue! 15 minutes of design and a little printing later, there you have it: a brand new magazine floor plate insert to allow full capacity in a SIG MPX magazine.
For obvious legal reasons, if you are living in a ban state, we do NOT suggest you modify your magazines to give them an illegal capacity. In general it is our strongest recommendation, should you choose to enjoy firearms, you do so in a safe, responsible, and lawful manner.
Scale can be a difficult thing to comprehend and convey. Numbers, sizes, and distances beyond a certain point start becoming intangible. Can you really picture in your head what precisely ten miles or a million of something looks like? Probably not, it is just too big to wrap your head around in most cases. So by example, we try to make scale relatable. (more on units/scale at the bottom)*
The Lance of Ra is the most powerful LED thrower ever produced. At almost 3 million candela, it is good for 2 miles of ANSI throw. That is a lot, and in an attempt to demonstrate that we did some photography showing it illuminating a spot on a mountainside 1.61 miles away, paired of course with a satellite image giving a sense of the distance.
But in that Lance photo there is another mountain ridge, just to the left of the one targeted. That ridge is part of a much MUCH larger mountain, which happens to be 4.27 miles away. Once again, for scale and measurement, we have a satellite image.
If you hadn't guessed by now, we're going to illuminate that mountain. We even have enough power in the wash to illuminate the "near" mountain which is "only" 1.6 miles away.
Welcome to the Light of Xiuhtecuhtli, named for the Aztec god of fire. With >50 million candela and >6000 lumens on tap, it is aptly named. This gives the LoX the power to reach out and touch targets 9 miles away (ANSI throw). It is a really unbelievable amount of performance, easily illuminating almost all clouds for example. Finding a place to really stretch its legs, and an evening clear enough to photograph it, was challenging. Ten mile visibility, the meteorological maximum air clarity standard, doesn't exactly occur between mountaintops nightly.
What else is out there which compares to the LoX you might be asking? Not much actually, the LoX may be the most powerful flashlight ever made. (flashlight being defined as a hand held light source) The current most powerful common thrower is the BLF Giga Thrower. A very popular light, the BLF GT spits out about 1 million candela give or take and about 2000 lumens. The very similar Astrolux MF04 does a little better at about 1.3 million candela, again give or take. The Maxabeam is also eclipsed several fold, which is a mere 12 million candela. The closest light in performance is the 52 million candela Maxablaster, which has about the same throw but at a fraction the lumens.
So where does the LoX stand? Right now it is a functional mule, a working test-bed for the optical and electronic architecture of the flashlight. This is why the numbers are all nicely rounded, this design is a long way from production, more performance may well be found if development is continued. Depending on customer response we may build this out into a complete product.
*Candela is lux (light intensity) relative to distance, as lux obviously will vary wildly with distance. While for technical reasons it generally shouldn't be measured at 1 meter, as it produces inaccurate results, 1 candela is defined as 1 lux at 1 meter. ANSI throw is a standard for converting candela into beam distance, essentially a level playing field for comparing how far a light will project a beam.