Suppressors and Gas Guns! My 2cents

[springer01]

Something else I have noticed and will share. My SBR in 300 AAC Blackout doesn't get near as dirty shooting suppressed as my .308. Maybe its difference in powder type or just the small amount of powder the Blackout uses to begin with, or a combination of both. But it hardly gets dirty at all running suppressed, which is nice because its super fun to shoot.

 

[Kilmore]

Wow, that is nasty! I spoke with Alan Brown the fouling/gas blowback issue on suppresed semi-autos. He told me they had fired many thousands of rounds to get the gas tube hole on the barrel the right size to avoid the fouling as seen on the photo above this post. My rifle doesn't even come close to fouling like that after firing 300 rounds without cleaning.

 

[MistWolf]

This thread got weird all of a sudden.

The thread didn't suddenly get weird, it started weird. There are a couple of statements in the first post that don't make sense. Note that I did not say the entire post didn't make sense.

It is not TOS to ask for clarification on statements that are not clear. It is not TOS to question statements that do not make sense, especially those that seem to defy the laws of physics. If my questions were not clear, tell me and I will attempt to clarify them

 

[Steelhead]

I have a couple questions



How do the gases exit the muzzle and sneak back into the bore? The gases are behind the bullet and are already in the bore



Could you clarify this point? It sound like you are saying that because of the fouling, cases do not stick to the chamber walls which increases pressure. If I am mis-understanding, please correct me



I understand that a suppressor increases the time it takes a rifle to blow down to atmospheric, but how does it make the pressure curve sharper? The pressure curve will be the same as an unsuppressed rifle until the bullet uncorks the barrel and the gases dump into the can. As the gases enter the larger volume of the can, pressure drops. Not as suddenly as being dumped into open air, of course but it drops nonetheless

I think what George is talking about here are the gases that are trapped in the suppressor. If the suppressor is ahead of the muzzle, now you have all these gases and burnt powder trapped inside the suppressor. After the bullet exits the suppressor, there's now two ways out....the exit hole of the suppressor and back into the barrel of the rifle, via the muzzle.

Now the question would be, which is the easiest escape route for those gasses and burnpowder smoke? You would think that the exit hole in the suppressor would be it, however, it's my guess that by this time the bolt carrier group is now starting to make it's way rearward, thus I would think that there is probably a suction effect going on as the case is being drawn back to be ejected. (besides the fact that some gases and burnt powder are going through the gas tube back to operate the BCG). This suction effect is drawing the gas/burnt powder smoke and particulate back into the chamber area.

As for the pressure.....I'm just guessing again......but it seems like you might have two drops in pressure and maybe another uptick in pressure. Once the bullet leaves the muzzle and enters the suppressor, the pressure would drop, but as soon as the gasses fill the suppressor, then the pressure is back up again. Once the bullet leaves the suppressor, then the pressure starts to go down again.

We have to remember too that there are gases ahead of the bullet, before it leaves the muzzle. (if you don't believe that, look at slow motion video of a gun firing). So these gasses will hit the suppressor before the bullet will. Do these gases that are trapped in the suppressor cause an increase in pressure? I would almost think that they would.

 

[-Nick-]

It's gets dirty real quick. I still shoot my 16" LR-308 suppressed though. I know the mess that I have to deal with.
For the guys that haven't shot a gas gun suppressed. This picture is the last two rounds in a magazine that was loaded to 10. The entire internals of the upper/lower looks much worse if you shoot more than a couple boxes of ammo.

CHRIS

You've might have some other issues going on then or it's the ammo you're using. Even after 18 rounds out of a 20 rounder with my can I don't get anywhere near that amount of fouling and I don't even have an adjustable gas block on mine.

 

[springer01]

You've might have some other issues going on then or it's the ammo you're using. Even after 18 rounds out of a 20 rounder with my can I don't get anywhere near that amount of fouling and I don't even have an adjustable gas block on mine.

Yeah I thought the same thing.

 

[HK MaNiaK]

Anyone have any experience with shooting a suppressor on an HK rifle, Ive read that they run great but not a good idea with subsonic because with the fluted chamber and back pressure its more likely for the round to stop in the barrel. I would figure carbon build up is not a problem for a G3 and they are already hard on brass leaving a dent and flute marks

 

[MistWolf]

I think what George is talking about here are the gases that are trapped in the suppressor. If the suppressor is ahead of the muzzle, now you have all these gases and burnt powder trapped inside the suppressor. After the bullet exits the suppressor, there's now two ways out....the exit hole of the suppressor and back into the barrel of the rifle, via the muzzle.

Ok, that makes sense

Now the question would be, which is the easiest escape route for those gasses and burnpowder smoke? You would think that the exit hole in the suppressor would be it, however, it's my guess that by this time the bolt carrier group is now starting to make it's way rearward, thus I would think that there is probably a suction effect going on as the case is being drawn back to be ejected.

There will not be any suction during blow down as the system is pressurized. That's why the gases are venting. The easiest route is the one that offers the least resistance.

After the bullet exits, the gases of course vent out the muzzle. After the bullet clears the bore and suppressor, the BCG finally pressurizes enough to begin extraction which unseals the chamber and what's left of the gases begin venting in that direction

As for the pressure.....I'm just guessing again......but it seems like you might have two drops in pressure and maybe another uptick in pressure.

The pressure drops as the bullet travels down the bore because the volume is expanding and I think gas temperature is dropping. Pressure will continue to drop as the gases fill the larger volume of the suppressor

We have to remember too that there are gases ahead of the bullet, before it leaves the muzzle. (if you don't believe that, look at slow motion video of a gun firing). So these gasses will hit the suppressor before the bullet will. Do these gases that are trapped in the suppressor cause an increase in pressure? I would almost think that they would.

Of course there is gas in the bore & suppressor before the rifle is fired. we are not shooting in a vacuum. Also, the bullet does not seal the bore perfectly so some of the gases will leak past the bullet as it's pushed.

The gas is expanding at approximately 5,700 fps. Of course, while in the bore, the gas cannot expand faster than the bullet allows. That's how the pressure is built up. Once the bullet uncorks the muzzle, the gases overtake the bullet. (That's why a good crown is so important to accuracy.) This gas passing the bullet is a large part of the puff of smoke seen ahead of the bullet in the slow motion videos

 

[Steelhead]

My earlier comments are mostly theories, however, have you ever notice the amount of smoke coming out of the chamber area when the last round is fired and the BCG is locked back? I've noticed it on my rifles. Sometimes it's more pronounced than at other times.

Next time I go shooting, I'm going to make it a point to look in the chamber area as soon as the last shot is taken. What will be interesting, is if the smoke is coming only from the gas tube or from the barrel.

 

[Steelhead]

Ok, that makes sense



There will not be any suction during blow down as the system is pressurized. That's why the gases are venting. The easiest route is the one that offers the least resistance.

After the bullet exits, the gases of course vent out the muzzle. After the bullet clears the bore and suppressor, the BCG finally pressurizes enough to begin extraction which unseals the chamber and what's left of the gases begin venting in that direction



The pressure drops as the bullet travels down the bore because the volume is expanding and I think gas temperature is dropping. Pressure will continue to drop as the gases fill the larger volume of the suppressor





Of course there is gas in the bore & suppressor before the rifle is fired. we are not shooting in a vacuum. Also, the bullet does not seal the bore perfectly so some of the gases will leak past the bullet as it's pushed.

The gas is expanding at approximately 5,700 fps. Of course, while in the bore, the gas cannot expand faster than the bullet allows. That's how the pressure is built up. Once the bullet uncorks the muzzle, the gases overtake the bullet. (That's why a good crown is so important to accuracy.) This gas passing the bullet is a large part of the puff of smoke seen ahead of the bullet in the slow motion videos

There was another thread talking about the BCG actually starting to unlock before the bullet exited. If I remember right that discussion got pretty heated too and I'm not sure if anything got resolved. There were video's in that thread too. I'll see if I can find it.

 

[Steelhead]

Here's a link to that thread about the bolt moving before the bullet exits the barrel. Look at the videos and see the gas coming back into the chamber.

http://www.snipershide.com/shooting/showthread.php?t=4845&highlight=unlocking+bullet+exits+barrel

These video's are without a suppressor.

Seeing these video's makes me wonder where is the easiest escape route for the built up gases to go? Out the suppressor or back through the chamber?

 

[Cixelsyd]

Yeah I thought the same thing.

Nah. It's not that TTI ammo I'm shooting.


CHRIS

 

[jimmykm21]

Killshot shoots a POF, which is a piston gun. He should get quite a bit less of the negative effects of shooting suppressed because the piston system doesn't directly dump all of the gas into the receiver. In my experience, piston guns still get dirty when shooting suppressed from the excess gas in the barrel. Not nearly to the same extent as a DI gun though.

I shoot a POF upper with a Gemtech and also switch it out to my DI rifle and can honestly say .
Other than both getting dirty , the POF also gets pretty filthy .

Both funtion fine after few hundred rounds on a good range day.
I never shot over 500 rounds in a day so I can't comment on extended shooting and both are 5.56 so maybe a 30 caliber might be different.