Yes, it can be legal to make a silencer. For everything Form-1, from silencer designs that are easily made, to filing forms with the BATF, to 3D modeling. Remember, you must have an approved BATF Form-1 to make a silencer. All NFA laws apply.
I've got a Gamo TC45, which is a .457 airgun, operating at around 3500PSI. Like the Airforce Texan, mine has a full length barrel shroud. But I am not so sure the design from the factory is helping much on sound suppression. Does it do some, sure, could it do more, I hope so. Airforce includes baffles, so lets assume for legal sake I am good to work on this without a form 1.
The shroud is 27.25". Threaded at the receiver with an o-ring, so sealed. The business end has the plastic cap shown, with the cone.
Shround ID: 35mm
The end of the barrel has an air stripper, with a main out hole of 14mm and 4 evenly spaced side vents of 8mm.
Past the air stripper is about 3.5 inches of air space. partially filled with the end cap cone.
What to do? Do I throw a couple k baffles between the air stripper and the cone/endcap? cut off the end cone and throw more baffles? Some of the airgun shrouds just have baffles made from felt wrapped around hair curlers. Is there any benefit in doing something with the shroud space, between the receiver and the air stripper?
Just to add, I do not expect I will get the 295gr slugs up above 800 fps. Still need to get my chrono out to the range. The 150gr pellets could get into the mid 950 range. With tuning I might get the gun up to 1000 fps
Anything above about 10fpe and felt wraps and hair curlers start coming apart. I had felt strips glued at the ends, loosely filling the void around K baffles in a 23fpe PCP in .22", and after roughly 1,000 pellets through it at that power level the felt started pulling into the bore in the first 3 baffles. Started opening out my groups, so I pulled the felt and accuracy came back. I recall trying hair curlers as spacers in a roughly 14fpe airgun years ago and they started compressing, distorting, allowing the washers between them to rattle. Plastic parts and fibrous fillers are probably a great help in suppressing very weak airguns but not appropriate in the kind of power range you're using.
800 to 1000fps is similar to .22lr subsonics, so yes, some K baffles would be appropriate. If you're able to make those, then I'd suggest also turning down the cone on that front cap. Keep a cone, it just doesn't need to be anywhere nearly that big.
Make sure your material at the bore is minimal - ie; when designing your K baffles make the transition between the two main parts as short as is practical such that you're not trapping expanding air in a series of tubes. Align your cross-bore vents neatly so air can push across and into the outer volume. Use a ball-end mill similar in diameter to your projectile, while making the baffle bores about 3mm to 4mm larger than that.
You could also use cones of course. Seems they do well for a lot of big bore airgunners. Whatever you use, the point is redirection, moving air off the bore so it can swirl around and lose energy. Part of it is acoustical in a direct sense, breaking up the sound waves by complex obstacles. Mere expansion into a space isn't enough. I've tried firing a pellet through a large can with just an endcap, and it's loud. Not as loud as with nothing on the muzzle, but not really suppressed significantly.
Is there a good rule of thumb for calculating how much space there needs to be in the baffle section? Right now, cone trimmed, I am looking at 3ish inches. But I am looking at making a shroud from carbon fiber and could go a few inches longer if that would help (vs shortening the barrel).
Also, is there anything to be done with the air stripper? More holes? Port them backwards? Also the shroud back of the air stripper is sealed, should it stay that way?
In the UK in the 1960s Parker Hale Made a short run of non-standard
can Model MM1 for .22 and air pistol.
I have brought up this off-beat design can that eliminated using their standard
circular Maximum model baffles entirely and in the front cap
they had a tube/snorkel protruding back into the can with, for the .22 round
an exit hole of 0.030" diameter.
For a .22 round it was not 'Dead Air Mask HD' quiet but it was just somewhat lauder than their standard disk
baffle model, also called MMM1. But on an air pistol its expansion chamber was
the whole internal can and then the air leaked out the tube. If memory serves
the snorkel went back about 2/3s of the can's length of about near 7" (?).
On a past gun site someone with this can surrounded the snorkel with
tightly packed metal scouring pads and got a good reduction.
Since you do have the front cap with an cone protruding back you could
tread a tube,with a. I.D. diameter greater than the pellet, into a tapped
and threaded hole into the front cap.
Just a thought.
Please let us know the test results whichever design you settle on.
ATXMH wrote: ↑Tue Aug 27, 2019 1:01 pm
Is there a good rule of thumb for calculating how much space there needs to be in the baffle section? Right now, cone trimmed, I am looking at 3ish inches. But I am looking at making a shroud from carbon fiber and could go a few inches longer if that would help (vs shortening the barrel).
Also, is there anything to be done with the air stripper? More holes? Port them backwards? Also the shroud back of the air stripper is sealed, should it stay that way?
3" isn't a lot for anything really. Takes the 'edge' off the noise, that's about it, even with state of the art baffles appropriate to the pressure/bullet involved. You'd probably see decent suppression with 6" of baffles, and 8" is likely ideal. Anything longer and it's not going to improve much, just bringing in potential harm to accuracy.
The plug should have a handful of holes drilled in it, front to back, such that blast chamber pressure vents back into the shroud. Otherwise it serves no acoustical purpose.
No idea about the air stripper, where it is, whether it's that big conical front plug... more information you could offer perhaps? Sounds like maybe it's at the back of that space, just in front of the muzzle, but I can't make out any details in that photo.
My Stoeger .22 air rifle had what I found to be a pretty weak suppressor. The 4 or 5 plastic baffles and the reflex design helped, but I was not happy. So naturally, like any red-blooded American with a brand new pellet rifle with an upgraded "Match" trigger, I put the chop saw to work cutting the whole thing apart ( I suppose ATF told Stoeger not to let their plastic suppressor be to easily transplanted to actual firearms, where it would then be considered a "bomb") I threaded the end of the barrel, and experimented. I found that the QD "airsoft" suppressors were more or less just simple expansion chambers, some with a foam insert. They worked about as well as the original integral design, and they were improved by using felt plumbing washers instead of the original open-celled foam. As long as I fire the heavier pellets, it stays subsonic, and pretty quiet, The mechanical noise of the springer design is much more noticeable ( Of course, it it right next door to your ear when fired) than the sound of the actual projectile launch, as near as I can tell. I gave up all hope of improving the design, since the only real gain for me would be to find a way to quiet the action.
In my holy war against the squirrels that torment my dogs in the backyard, I now use my 10-22, fitted with a 30 inch barrel. It has the ultra-light bolt kit, so it can fire ( Feed and auto-cycle) CCI "quiet" rounds, but these are still at 911-call sound levels, so I use a .22 Short magazine and hand-cycle Aguila Colibri rounds, which are as quiet as you can get, especially in a 30 inch barrel ( Nope, no squibs yet!) and within 50 feet, the squirrels stand a sporting chance of survival, but at least I have avenged my dogs, who have had to go on doggie-prozac to deal with their rodent-induced PTSD. I am still searching for the optimum OSS quality squirrel "final solution". Maybe I need a pet owl...
FYI, a blue 15 Watt laser seems to attract the squirrels, and burn them a little at 30-40 feet, which makes them at least a bit more cautious. It has the unfortunate side effect of occasionally setting my backyard on fire.
