Suppressor that closes after bullet leaves?

Has anybody ever designed, made or tried to build a suppressor that seals the exit hole after the bullet leaves to trap gas inside? Obviously timing would be the tricky part, assuming it doesn't blow up.

EDIT: never mind, I misunderstood what you meant

The closest is the Russians with their "gas trap" cartridges. They are special rounds of ammunition that have a piston behind the projectile. When the round is fired the piston propels the bullet forward out of the weapon, the piston is retained inside the cartridge case trapping the gas within and incidently silencing the weapon. I can't remember the nomenclature for the rounds or the specialty weapons that fire them. They were used by the KGB and whatever replaced it (FSV?) mostly and Spetznaz units seconded to intelligence work.

Someone in Afghanistan got a hold of one of the pistols and some rounds and Small Arms review sent a reporter out to shoot/study them. They did a write up on it about a year or so ago I think.

The expended rounds incidentally become very small high pressure vessels and are somewhat dangerous to have around for a few months while the gas slowly leaks out. ATF was contacted by someone thinking about making similar rounds in the USA and decided that if any were produced here each round of ammunition would count as a suppressor and require a $200 tax stamp. That pretty much ended that idea.

Use of the expanding gas to actuate a lever that closes a door behind the bullet is what i had in mind. It would have to work incredibly fast in order to trap the expanding gasses the moment the bullet leaves which may be impractical but its just a thought.

Sounds like you would a specially designed host weapon for that system, since with an unmodified weapon the gas would just go back towards the chamber and from there to the rest of the gun. Could get exciting.

I thought about that and also had the idea of a trap door on both ends the muzzle to reduce back pressure. The other thought would be baffles that sort of close, trapping gas inside until pressure returns to normal. Timing is of course the trickiest part.

Congratulations, you have reinvented the wipe.
I bet modern materials and some rocket science on the thickness and contour would give better results than the old sheet rubber. And no moving parts.

Congratulations, you have reinvented the wipe.
I bet modern materials and some rocket science on the thickness and contour would give better results than the old sheet rubber. And no moving parts.

What i'm discussing entails moving parts and is quite different than a wipe. I'm talking about a chamber held open, probably by a spring, that is momentarily closed by the pressure of the expanding gasses.

I know that is what you are talking about.
Kind of like an excess flow valve that slams shut when the fluid going through starts moving too fast.
I am not optimistic about moving parts in a hostile environment.

Using gases to operate other things is not a new idea on guns.

http://files.abovetopsecret.com/files/img/km4f2f5f24.png

A simple way would be to make something like a spring loaded veg steamer. Bullet would pass through a hole in the center then gas would close the hole until the pressure lowered. The hard part would be making it hold up to the pressure and not gumming up and sticking.

http://www.foodsteamerreviews.com/images/stories/food-steamer-images/food-steamer-vegetable-steamer-2.jpg

I know that is what you are talking about.
Kind of like an excess flow valve that slams shut when the fluid going through starts moving too fast.
I am not optimistic about moving parts in a hostile environment.

Like inside an AR? True, fouling could eventually impair function however with modern materials it may be a low enough hurdle to overcome.

As i see it the real challenge is timing. Especially if different rounds are used with varying pressures.

Using gases to operate other things is not a new idea on guns.

I'm not sure what that statement is meant to contribute. That vast majority of new developments in self loading guns has been just a new or improved method of utilizing the expanding gasses. And?

Sounds like the suppressor would need to be a seamless part of the barrel; internals of the suppressor rifled just like the rest of the barrel with ports cut to relieve gas into the chambers. This would prevent high pressure gases from passing the bullet in the suppressor and help with your timing issue.

Just spit-balling, but here's an idea:

You could perhaps make some kind of integral suppressor that used ports with check valves to reduce the uncontrolled release of gas. Basically a suppressor is just a place to allow gas to partially expand before release to the atmosphere which lowers the pressure and reduces the "pop" of the uncontrolled release from the gas stored in the suppressor and bore. If you used check valves, you could capture the gas within the suppressor (the vast majority of the gas generated) and only the gas in the bore would be released as the bullet left the muzzle. The gas trapped in the suppressor would leak out of smaller holes over a greater period of time to diffuse the noise.

Probably wouldn't be very good for rapid fire though as the suppressor would build more and more pressure if you shot faster than it could let off pressure.

I'm not sure what that statement is meant to contribute. That vast majority of new developments in self loading guns has been just a new or improved method of utilizing the expanding gasses. And? No "and" that was my point.

There really wouldn't be a "timing" issue as long the "check valve" didn't close by the air being pushed out of the barrel by the advancing bullet. The expanding gas is behind the bullet. There are some high speed videos of a clear monocore suppressor on youtube you might take a look at.

The closest is the Russians with their "gas trap" cartridges. They are special rounds of ammunition that have a piston behind the projectile. When the round is fired the piston propels the bullet forward out of the weapon, the piston is retained inside the cartridge case trapping the gas within and incidently silencing the weapon. I can't remember the nomenclature for the rounds or the specialty weapons that fire them. They were used by the KGB and whatever replaced it (FSV?) mostly and Spetznaz units seconded to intelligence work.http://en.wikipedia.org/wiki/OTs-38_Stechkin_silent_revolver

The USA experimented with "QSPR" revolvers and captured-piston cartridges in the late '60s for "Tunnel Rats" in Vietnam.

As i see it the real challenge is timing. Especially if different rounds are used with varying pressures.That's my take too.

It's going to be tricky to make sure it closes quickly enough to be worthwhile but not so quickly as to clip the bullet. I think it would have to be set up to work on one particular firearm and with one particular loading.There really wouldn't be a "timing" issue as long the "check valve" didn't close by the air being pushed out of the barrel by the advancing bullet.There's definitely a timing issue if you want this thing to be of any value.

It's one thing to have a valve that closes after the bullet leaves, quite another to have one that closes fast enough to trap sufficient gas behind the bullet to make some sort of reasonable difference in the muzzle blast noise but not so fast that it tries to catch the bullet.

The former is very simple. The latter is complex and timing will be critical--everything hinges on the timing.

Remember, the gases will escape at velocities much higher than the bullet velocity, once the bullet clears the bore. This valve would need to close almost immediately behind the bullet to catch enough gas to make a practical difference in the muzzle blast.

In regards to the suppressor trapping gasses to reduce sound signature...you will ultimately have a "leakage system" so to speak, that bleeds off the held gas slowly.
So to play devils advocate, are you ok with only firing one round every five minutes to allow for bleed off of pressure? Or were you looking to build a pipe bomb on the end of a muzzle?

Keep in mind that a long, hissing, release of pressure may draw more attention than a short, staccato, cough or spit sound.

Just sayin'

I think this is what you are looking for

From Wikipedia:

The Welrod was a British bolt action, magazine fed, suppressed pistol devised during World War II at the Inter-Services Research Bureau (later Station IX), based near Welwyn Garden City, UK, for use by irregular forces and resistance groups. Approximately 2,800 were made.

More details available here http://www.timelapse.dk/thesilencer.php. The life of the silencer in this device was limited as the washers wore out due to the friction of the bullet. I seem to remember reading about leather seals being put at the end of the muzzle to close up after the bullet left but I cant remember where.

I think this is what you are looking for

I was thinking along the lines of a devices that makes no contact with the projectile and uses expanding gasses to actuate a lever or other mechanical device to close off the exit hole of the suppressor.

Sound like a pretty tough proposition. It would have to be pretty big, to pack in strong enough components to stand up to the pressure. Then what happens if it fails? Unless you are the manufacturer, you have to send it back to get fixed, as a person with a suppressor cannot have extra parts for it. If you are the manufacturer, are you gonna service all of them when they break?

Not saying its impossible, but very highly improbable to make something worthwhile.

I once spoke to a guy from New Zealand about suppressors years ago. He mentioned that they had a type where a piston type valve was used to trap gasses by way of the pressure moving the valve (which was under spring pressure), and as soon as it dropped just a little the spring returned the piston type valve to seal the vent holes. I don't know how well it worked, but it sounded like it might seal off at least some of the gases from further expansion.

Well lets think about this for a second - It takes a significant amount of gas, moving at a fairly fast speed to propel a bullet at 700+fps... Do we REALLY want to stop all that gas in the gun (more or less) that we're holding in our hand, near our face?

You go ahead with your "closing suppressor" idea - I think I'll stick with something that has a hole at the business end instead of a valve that opens and closes - it might be louder, and it might be quieter, but your idea of blocking off the gasses like that seems to me no better than playing "chicken" with M-80's as kids (I know at least 2 people that have lost a finger or fingers doing that stupid stuff 20 years ago).

I once spoke to a guy from New Zealand about suppressors years ago. He mentioned that they had a type where a piston type valve was used to trap gasses by way of the pressure moving the valve (which was under spring pressure), and as soon as it dropped just a little the spring returned the piston type valve to seal the vent holes. I don't know how well it worked, but it sounded like it might seal off at least some of the gases from further expansion.

Do you know if the gas was trapped in the baffles or was the suppressor itself sealed off? Both ideas have been rolling around in my head with the first seeming more practical but less effective.

You go ahead with your "closing suppressor" idea - I think I'll stick with something that has a hole at the business end instead of a valve that opens and closes - it might be louder, and it might be quieter, but your idea of blocking off the gasses like that seems to me no better than playing "chicken" with M-80's as kids (I know at least 2 people that have lost a finger or fingers doing that stupid stuff 20 years ago).

Reminds me of the people who said the human body could not withstand going faster than 30 mph.

Well lets think about this for a second - It takes a significant amount of gas, moving at a fairly fast speed to propel a bullet at 700+fps... Do we REALLY want to stop all that gas in the gun (more or less) that we're holding in our hand, near our face? The gas pressure that exits the muzzle is lower than the pressure at the chamber (the part just a few inches from your nose when you shoot a rifle). Instead of pressure I would worry about a bullet impact with a fouled "valve".

http://www.youtube.com/watch?v=otpFNL3yem4

I think it would be particularly tricky given that gas (albeit lower pressure) escapes ahead of the bullet as well

I think it would be particularly tricky given that gas (albeit lower pressure) escapes ahead of the bullet as well

Certainly all gas could not be captured. Existing air in the barrel will of course get compressed by the bullet and some gas may leak past due to grooves from rifling however i think this is extremely minimal. The question is could the trap close fast enough to capture enough of the gas to suppress better than a conventional baffle method.

I actually saw the drawing of it, and it was like a piston chamber inside the suppressor that opened the holes to the chamber when the blast hit it, and then the spring rebounded, and the chamber moved to seal the expanded gases in. Bear in mind, it didn't trap ALL the gases; there were baffles forward of the piston/chamber.

The question is could the trap close fast enough Check valves commonly used for compressed gases work at the rate of opposing flow. I think "the question" is back on post #15, can you design a valve that would not close before the bullet passes but close before all the gas excapes. If the valve closes from the air moving infront of the bullet your out of luck.

Humbert, a Frenchman, came up with this basic idea in 1898; he proposed designs for both artillery and small arms, but I don't know if any were actually built. He suggested using either a "clapper" that would be sucked closed by the passing bullet/shell, or a lightweight ball that would do the same (but I don't know what he would have suggested if you had to fire downhill). This photo is from Semyon Fedoseyev's "Spetsnaz Oruzhie"/"Special-purpose Weapons".

Good find, SDC. Thanks for the pic. The ball idea is very interesting and not something i ever considered.

Thats how many check valves work but me either...

Thats how many check valves work but me either...

True but the method above essentially turns the entire can into a check valve.

Not sure what kind of firearm you're looking to put it on but thinking off the top of my head...

but If there were a large "flap" on the end that is under spring pressure(it swings OUTWARDS away from the muzzle), what if a small gas chamber were routed from the barrel(roughly mid-way... bullet needs to get moving first) outwards to the flap so that the pressure forces it outwards... as long as the gas tube is sized right, and the actuating portion is sealed well enough, then pressure should still remain in the barrel overall until the bullet leaves the muzzle, at which point pressure will equalize and it will close again.


You could also substitute the "flap" idea with a "sliding" blocking plate actuated by piston(s) and it would function the same.


That said, I don't think ANY idea will FULLY close the suppressor in question and gas will need to be allowed to leak out due to pressures inside the barrel.


Something a bit more doable(albeit not fully mechanical if that's something you're after) might be to drill a gas tube to host a piston, and use that piston to actuate an electronic microswitch that will control a solenoid valve that will actuate the blocking mechanism(whether plate or tilting whatever you decide on).


Just throwing some ideas out there:cool:

If this thing can actually be made to work, it's going to be problematic with semi-auto rifles. You won't want to eject the cartridge while there's pressure still being held in the chamber/bore.

Check valves commonly used for compressed gases work at the rate of opposing flow. I think "the question" is back on post #15, can you design a valve that would not close before the bullet passes but close before all the gas excapes. If the valve closes from the air moving infront of the bullet your out of luck.

Yes, that was my concern - it ups the trickiness factor of an already very finicky set up - would have to cut a very narrow window of pressure

but If there were a large "flap" on the end that is under spring pressure(it swings OUTWARDS away from the muzzle), what if a small gas chamber were routed from the barrel(roughly mid-way... bullet needs to get moving first) outwards to the flap so that the pressure forces it outwards... as long as the gas tube is sized right, and the actuating portion is sealed well enough, then pressure should still remain in the barrel overall until the bullet leaves the muzzle, at which point pressure will equalize and it will close again.

Do mean an external flap? Interesting idea. Also if the system malfunctioned the bullet would likely be able to force its way through if designed accordingly. If attached externally it may also allow for a retrofit to existing cans although a gas tube running outside may not be ideal. It would certainly make it easier to test the concept.

A good question is would installing a flap to the exterior of an existing can require any sort of registration with the ATF.

If this thing can actually be made to work, it's going to be problematic with semi-auto rifles. You won't want to eject the cartridge while there's pressure still being held in the chamber/bore.

I think the question will be how much pressure would remain during ejection as opposed to if all is gone.

There's enough pressure remaining in the bore to make a sound like a small explosion or this entire discussion would be moot, right?

I wouldn't want that much pressure propelling an empty case out of an open action nor acting on a bolt that has unlocked in preparation to eject the fired cartridge.

There's enough pressure remaining in the bore to make a sound like a small explosion or this entire discussion would be moot, right?

Use of a convential suppressor can increase ejection force due to back pressure. The question is whether or not the pressure falls to within acceptable levels in time. Trapped expanding gas from combustion does not remain at high pressure indefinitely.

Trapped expanding gas from combustion does not remain at high pressure indefinitely.An action typically unlocks and ejects within just a few milliseconds--not exactly "indefinitely".Use of a convential suppressor can increase ejection force due to back pressure.Sure, but a conventional suppressor is trying to give the gases a place to go so other than out the muzzle and to slow the escape of the gases. It's not trying to trap them outright. There's a huge difference in the two functions.

But yes, even the relatively small increase in back pressure due to a suppressor can have an adverse effect on function. If one could actually manage to trap the gases with a valve, that would cause much higher pressures.

Even if it were possible sounds like it would be prone to breakage.

The gas trap rounds sound neat, going to have google up on those

An action typically unlocks and ejects within just a few milliseconds--not exactly "indefinitely".

And gas pressures from combustion, even if trapped, rapidly decay. I do not know if they do so fast enough or not and it is a valid concern. Obviously the can would not be able to trap all gases. It may be an issue in some guns and not others or may require an adjustable gas system. For example, a 20" ar may work but not a 14.5".

Even if it were possible sounds like it would be prone to breakage.

I think that depends completely on how the thing works. Modern materials certainly make it more feasible today than in the past.

best thing is the kiss principal on suppressors.if there is moving parts,they will break at the most inopportune time.they have to be made indestructible and as sturdy as possible as field oporatives who would be using them in most cases would not be mechanically inclined and unable to do field repair.

I was referring to an external flap as you thought...

My thinking isn't so much to stop all gasses(not going to happen), but the flap may assist in directing the gasses(and sound) downwards... similar to cupping your hands to throw your voice in a similar direction(and consequently lowering the volume in other directions).

It could also go upwards if you wanted... depending on if you're shooting indoors or out would probably make you choose to do one or the other.

Worst case scenario, maybe the bullet hits the flap and it breaks(I'd recommend something LIGHTWEIGHT so it is more likely to be moved by the bullet IF this were to happen than if it were heavier).


On a related note... ASSuming you're trying to make it quieter so it's less detectable for whatever it is you're shooting AT... why not build a suppressor like normal, with a muzzle-brake on the end to redirect the remaining gases?

Depending on how it is dispersed, I imagine with a large enough brake, with pressure relief holes/slots/whatever all the way around the circumference of the barrel, in my head it seems it would make sense that by redistributing the sound of the propellant gases to go in all directions(instead of just forward from the muzzle) it may be quieter for anyone in front of the muzzle... maybe with a slight increase in noise from behind/to the side of it though.

Again, just thinking out loud.

And gas pressures from combustion, even if trapped, rapidly decay. I do not know if they do so fast enough or not and it is a valid concern.For safety, the chamber is not supposed to open/the action is not to unlock until the bullet has left the bore.

If this device is fast enough to trap enough pressure to significantly reduce the report, it will also cause the barrel pressure to stay at levels high enough that it would be unwise to unlock the action/open the chamber until that pressure is reduced. If this device is to be useful for its intended purpose, it will not be applicable to semi-auto actions because they open the action very rapidly. That's without getting into the issues involving what retaining pressure in the barrel would do to a gas system.

By the way, I'm still predicating all my responses with "If" because I still don't think it's feasible in the first place. I'm just pointing out that even if it were somehow manageable, it would cause other problems in certain types of actions.

My thinking isn't so much to stop all gasses(not going to happen), but the flap may assist in directing the gasses(and sound) downwards... similar to cupping your hands to throw your voice in a similar direction(and consequently lowering the volume in other directions).

Couldn't you get the same effect with just a hood protruding out over from the top of the can?