a_canadian wrote:Has anyone built a .22lr can get using similar principles to what is used in those sound laboratory negative decibel rooms? I can see such long conical shapes being adapted for use in a rimfire can in a couple of ways: welding hollow pencil-tip-like cones (or perhaps elongated pyramidal cones) into thin tubular rings and stacking these as a series of 'baffles' (probably best to put one or two washer type baffles in there too), or rendering long thin cones as the complex internal structure of a monolithic sintered metal 3D printed device. Perhaps I've missed such experiments, but in years of looking at cans online I've yet to see anything like that. Seems bound to absorb sound and break it down via complex destructive interference, more effectively than K baffles perhaps.
Owing to the cones converging in a cylindrical suppressor tube it would likely prove more effective if done in a rectangular body. Easier for assembly as well. Just spread flux on a piece of sheet metal (oversize to prevent warping due to heat) and lay out your grid of cones within a marked rectangular area, then sweat in a layer of silver-bronze alloy rod with a torch, then trim to shape and tig weld four of these panels together. A bit fussy figuring out how to achieve a proper bore placement and size but not rocket science. I'm guessing such a pattern could be scaled for various levels of suppression efficiency just using smaller or larger panels and cone sizes. Tricky too would be cones interfering with each other... So maybe an alternating grid pattern from just two sides if using longer cones, or stick to shorter ones and have them on all four sides.
Another notion; do the same as above except with a single sheet of steel, alternating 8 rows in a zigzag pattern. Trim to finished length and width after it cools, then crease 7 times between the rows and fold the thing together for an octagonal can with maybe 100 little teeth facing each other. Make them tornado shaped for increased air volume. Weld on end caps and you're done.
While all sound is pressure, the particular sound of gunshots is the suddenly escaping ("uncorking") pressure, same as rupturing a pressure vessel, disconnecting an air hose, air guns, etc. Suppressors don't work by mitigating the acoustic waves like a dead room, but by slowing the flow of the gasses that are uncorking, giving them more time to cool & contract, ergo reducing the pressure that vents out the front.
See DKDravis reply, he explained it well.
One of the challenges faced in trying to bring the SPL much lower than we've managed to so far is the fact that there's no way around having a hole right through the center of our muffler. The noise produced by an IC engine can be just as high (sometimes higher; nitromethane dragsters will meter 150+ dB at 100 feet or more) than a gunshot if measured right at the exhaust port or short tube off of it. But the amount of length & volume, and being able to completely eliminate laminar flow by making all
of the exahaust gasses change direction are why we can take the noise of an IC engine combustion cycle from 150 down to 80.
The other challenge is making it practical; if it's 2 feet long and weighing 5 pounds, I don't care how quiet a suppressor is, I'm not interested, and I would wager that I speak for the overwhelming majority of the market. Sales trends indicate that 1.5x 8" is about the most people will readily tolerate on handguns or sporting rifles, with 1.75" x 9"-10" being the upper end of what will sell at all other than necessarily monstrous 12 ga and .50 BMG cans. I know the idea behind this thread is what can be done at all, not what can be done practically, but I don't feel you can divorce possible and practical to that degree where firearms and suppressors are concerned. To wit, we wouldn't even be discussing the semi-auto if quietest possible gunshot were the single important factor. Running with that, what's the point of an uber-quiet semi-auto if it can't be made reliable and practically useful?
Many of you haven't known me long enough to realize that the work I do is well more than building silencers and threading barrels. I've built some of the lightest weight prototype rifles you're likely to ever encounter, from a 3.48 pound autoloading 9mm carbine to a 19 ounce
.22 bolt action (both title I, not SBR). Are they absolutely as light as could be done? Of course not. They are, however, as light as can be made practicably from a durability and utility standpoint. I see little use in pushing the limits of possible to end up with something completely impractical or unworkable. I would make it analogous to the automotive world r.e. the aforementioned nitro dragsters; they make over 10,000 HP and accelerate to more than 300 MPH in less than 4 seconds. Is that the most horsepower possible from a big, supercharged nitromethane V8 engine? Not even close. But what's the use in having 15,000 horsepower if it can't be put to the ground due to limitations in traction? The answer is none. And that's why, while I still consider it an interesting mental exercise, I won't personally invest time and energy into developing a suppressed weapon system that gives up portability, usability, reliability or durability to shave a few more dB from the total noise. With semi-autos, even if you manage to deaden the sound of the bolt reciprocating and stopping, you still have rounds being stripped from the magazine and pushed into the chamber, and while I don't have dB figures on doing that even by slow manual action, consider the noise made in cycling any bolt action rifle. I would wager that even with little bumpers that all but eliminate the noise from the bolt hitting the breech face, you're still gonna be near if not over 100 dB dropping the bolt on any rimfire autoloader. I'll check that and post back once I have my new mic for the B&K meter.
As well, the practical and possible limitations of reducing autoloader action noise are further compounded by the significant perception of suppressors already being the tool of an assassin. It's been fairly easy to counter that with videos and explanations that demonstrate real world suppressors being far from the Hollyweird representation and using that in conjunction with data showing what is hearing safe. It's pretty easy to defuse even the most rapid anti's arguments by pointing out that the typical suppressed gunshot is in the 115-140 range, making the firearm safer to use but far from audibly undetectable. I think in the current climate, we would actually do ourselves a disservice to make highly specialized weapon systems that are so quiet you actually can't hear the shot from the next room.
All that said, I think if you wish to effectively reduce the action noise much below the sound of the actual shot, you need to be looking in a completely different direction. As in, rather than trying to limit the SPL of mechanical noises, how to not make them in the first place. The short answer is that you're not going to accomplish that well if you continue to address it with firearms that use gas or recoil energy to cycle the action. What you essentially want is a manual action that is cycled automatically, and you get that with electronics. With electric motor driven autoloading systems, you can eliminate every fast-moving spring-dependent mechanism but the striker or hammer (that, too, with electronic ignition like Remington E-tronix). You can program it to not cycle for however many milliseconds after the shot to let bore pressure attenuate, eliminating port noise. You can have the bolt unlock & move at any speed you want. You can have the rounds presented before the chamber in a number of fashions that will minimize or even elimate the noise of stripping them from a magazine. You can have buffers & bumpers in place which deaden any remaining mechanical noise which wouldn't be possible due to durability with a completely mechanical action, but with the slower movement of a servo action, can actually last. You can tie the ejector into the electromechanical system so that it is more a remover, even something like a little arm that pushes the spent case into a cavity in a piece of foam attached to the port. And you can do all this with a pretty normal looking firearm, without any particularly unusual or cumbersome apparatus.