B Recoil dampening in silencers and supressors

[microcuts]

TL;DR Summary

What makes silencers and supressors dampen recoil - how does it work?

Hello, I have a physics question. It is firearm related.

It is said that a silencer/supressor has an unintended side effect in that it will reduce recoil. I am not talking about recoil reduction due to added weight; apparently if you stuck a deadweight instead of a silencer/supressor, you would not gain same recoil reduction. Instead, due to the rapidly moving explosion of the propellant, the movement of the explosion hitting the baffles of the silencer pushes the gun forward, thus reducing the kickback. Oh and baffles are basically conical tapers that face away from the origin of the explosion, kind of like V's.

You can take a look at inside of silencer here https://1s18w12tqveh1xfywp1ulx42-wpengine.netdna-ssl.com/wp-content/uploads/4-0014.jpg

What I don't understand, is how does that work? My current guess is, as the gas molecules smash against the surface of the baffles, they provide forward momentum. Where I get confused is, unlike a muzzle, they have nowhere to escape, so it seems like after bouncing on the surface of the baffle, they would have no choice but to bounce back on the opposite surface which to me would seem like it would negate some of this recoil reduction, unlike a muzzle break would, where after hitting the surface of muzzle they would fly off into atmosphere around, not on the parts of the gun. Unless, on that initial impact, they lose a good chuck of momentum driving the gun forward, and don't hit as hard on the return movement. Does any of that make any sense to anyone?

If someone could shed some light on why and how this all works, I would really appreciate it, even guesses are welcome.

Thank you.

 

[anorlunda]

I found this. It suggests that some people confuse flash suppressors with muzzle breaks. Is that the case here?

A flash suppressor is different from a muzzle brake, although they are typically mounted in the same position and sometimes confused with each other. While the former is intended to reduce visible flash, a muzzle brake is designed to reduce recoil inherent to large cartridges and typically does not reduce visible flash.[1]

 

[jrmichler]

The burned gunpowder has both mass and velocity, therefore contribute to the recoil. The silencer traps the gases and releases them "slowly", thus reducing their contribution to recoil. There is a good discussion of recoil in Hatcher's Notebook by Julian S. Hatcher, where he states "...over one fourth of the recoil velocity of the average high powered rifle is caused by the rocket-like thrust of powder gas that rushes out at high speed as soon as the bullet leaves." That book has almost 50 pages on the subject of recoil and is highly recommended if you are interested in the subject.

 

[Mark44]

@microcuts, you're asking about two more-or-less unrelated phenomena. A flash suppressor's purpose is to reduce or minimize the visual flash emitted from the firearm, so that an opposing rifleman can't determine where the shot is coming from. A silencer's purpose is to reduce the sound emitted from the firearm using baffles, similar to what a car's muffler does.

A muzzle brake diverts some of the escaping gas to counter the tendency of the firearm's barrel to rise after each shot.

apparently if you stuck a deadweight instead of a silencer/supressor, you would not gain same recoil reduction.

Actually, I believe there would be some reduction in recoil. Recoil force is directly related to the mass of the firearm. For a given cartridge size, a lighter firearm will have a larger recoil than a heavier firearm.

 

[microcuts]

I found this. It suggests that some people confuse flash suppressors with muzzle breaks. Is that the case here?

No, I don't think I'm confusing anything.

@microcuts, you're asking about two more-or-less unrelated phenomena. A flash suppressor's purpose is to reduce or minimize the visual flash emitted from the firearm, so that an opposing rifleman can't determine where the shot is coming from. A silencer's purpose is to reduce the sound emitted from the firearm using baffles, similar to what a car's muffler does.

A muzzle brake diverts some of the escaping gas to counter the tendency of the firearm's barrel to rise after each shot.

I am asking about unintended side effect of the silencers/suppressors. I am aware that this is not their primary purpose. I am curious to understand how this side effect works.

Actually, I believe there would be some reduction in recoil. Recoil force is directly related to the mass of the firearm. For a given cartridge size, a lighter firearm will have a larger recoil than a heavier firearm.

Yes, of course, adding weight will absolutely always dampen perceived recoil. That is not what I am curious about, however.

The burned gunpowder has both mass and velocity, therefore contribute to the recoil. The silencer traps the gases and releases them "slowly", thus reducing their contribution to recoil. There is a good discussion of recoil in Hatcher's Notebook by Julian S. Hatcher, where he states "...over one fourth of the recoil velocity of the average high powered rifle is caused by the rocket-like thrust of powder gas that rushes out at high speed as soon as the bullet leaves." That book has almost 50 pages on the subject of recoil and is highly recommended if you are interested in the subject.

That's the thing, a lot of people argue that it merely distributes the total force of recoil over a longer period of time, but, here's a video of a guy testing different attachments to see how far the gun gets pushed back :



Now, some may argue that it was only the weight of the attachment reducing the travel distance (and honestly the guy setting up the test should have accounted for that keeping the mass of the whole system consistent throughout the test) but it looks to me that recoil was not just made gentler, the gun actually traveled less distance, thus, some of the energy of the forward blast was actually used to force the barrel forward, reducing the recoil. But since the weight wasn't factored in, I cannot reliably say so since it could have been simply the mass of the silencer doing this.
However the author states that adding 60 - 350 grams wouldn't have made that much of a difference, in his opinion.

Thank you for the book recommendation, I will actually look into it.

 

[Nugatory]

Momentum is always conserved, but kinetic (as opposed to total) energy is not. It seems likely that some of the kinetic energy of the forward-moving stream of gas is absorbed by and heats the silencer baffles. The sum of the backwards momentum imparted to the gun (this is the recoil) and the forward momentum of the gas stream must be zero, so turning some of the kinetic energy of the gas into waste heat will reduce the recoil.

 

[Klystron]

I presume the OP uses the term "suppressor" in the modern sense of "sound suppression" to replace the popular but inaccurate term "silencer".

Sound suppression techniques include using subsonic ammunition implying, though not limited to, reduced propellant load; various modifications to chamber and barrel designs; and various ports and baffles both intrinsic and added to the firearm. Flash suppression and flash suppressors are closely related devices to sound suppressors often pinned to a rifle barrel; less commonly to handguns.

Conversely, sound suppressors, despite popular use in films, are probably more effective in handguns where subsonic ammunition would not significantly impact projectile range and mission requirements. Note also automatic and semi-automatic firearms where propellant gases actuate mechanisms providing a limit to propellant reduction.

 

[GravelFox]

Without numbers describing the recoil reduction it isn't possible to work out a precise explanation, but I think you can understand the problem just by considering conservation of momentum.

When a firearm is fired, the bullet and expanding propellant (not explosive!) are all, or mostly all, expelled through the muzzle of the barrel. They have mass, and because they are moving with respect to the firearm they possesses some momentum that influences its motion. When a silencer is added to the end of the barrel, such that it encloses the expanding gases and diminishes their momentum, there is some reduction in rearward recoil.

Example: I load a cartridge with an 11.33 gram (175 grain) bullet and 2.85 grams (44 grain) powder and fire it in a barrel that gives that loading a bullet speed of 853 m/s (2800 f/s). The gases created by the expanding powder should have a "first approximation" momentum around 2430 grams*meters/second. The bullet will have momentum around 9660 grams*meters/second, or around 4 times that of the powder (11.33/44 = 3.98). The bullet passes the silencer unobstructed, and (we assume) the expanding powder is completely retained until its speed is diminished to zero. So for our cursory solution we expect a reduction of felt recoil by about 2430/(2430+9660), or 20%. Of course, a real silencer wouldn't reduce the speed of the expanding powder completely to zero, so the expanding powder is expelled at some speed we don't yet know, and that causes an amount of recoil. Also, the cartridge case and barrel both have volume, which mitigates how much of the expanding powder reaches the muzzle, so that affects the real solution as well.

 

[hmmm27]

It's worth mentioning that the purpose of a flash suppressor is to preserve the eyesight of the shooter.

 

[John Archer]

I suspect a silencer (slightly) reduces perceived recoil by spreading the recoil impulse out over a longer period of time.
In addition to muzzle brakes, compensators (mostly used in pistols) use the gasses to direct the barrel downward to reduce muzzle flip.