AR 15, back pressure and suppression?

[bobhaverford]

On another thread the following statement was made: SR-25 has the same probs as all the other AR tack drivers. When suppressed, the increased back pressure blows all the crap back into the chamber. This is not amusing on my AR-15, and it'll be worse in a .308 AR. The exception would be if a company used the op rod system i've seen for the HK AR-15 uppers on a .308 upper.

What does he mean by suppression and what does he mean by blowing all the crap back into the chamber? I'm thinking about purchasing a DPMS 308 and was wondering if this was some kind of design flaw?

Thanks.

 

[Lebben-B]

"Supressed" as used in the context of your post refers to a sound supression system, a silencer if you will.

If you're not going to buy a silencer for the DPMS, the rifle will be fine.

Mike

 

[444]

Suppression as in a sound suppressor, aka a silencer.
If you are not using a suppressor, then disregard.

When I fire my AR with a suppressor, so much crap is blown back into the action that the unfired ammo in the magazine is covered with black soot. Some people have it so bad that they can't fire the rifle without glasses. Someone sells a nylon looking thing that goes over the back of the aciton to keep this gas out of your face. I use a PRI Gas Buster charging handle and don't notice it on my face, just in the gun. I am not sure if this is an AR specific issue or not. I never used a suppressor on any other centerfire rifle. To me, it isn't a big deal. So the rifle gets dirty ? So what ? It is getting dirty anyway. It doesn't impair function or anything.
And, it isn't being blown back in the chamber, the guy is trying to be dramatic. Where did you read this ?

 

[Lebben-B]

Gas blowback with AR type weapons is common, particularly with shorter barreled versions, due to the direct impingement system. Without the can, most of the excess gas is expelled out of the muzzle and some from the gas tube as the BCG moves rearward. With the can and a short barrel, more of the gasses remain in the bore after the round leaves the weapon. When the bolt unlocks and moves rearward, the gas and carbon blows back into the chamber and receiver.

Mike

 

[Zak Smith]

I've shot a gazillion rounds through a Gemtech M4-96D on both a 17" and 14.5" AR15.

I've never had a reliability problem due to increase blowback, but the upper does get "dry" and dirtier faster.

As far as gas blockback bothering me the shooter, I only notice it when shooting a lot of rounds from a single position, especially when there is no wind.

You should always be wearing eyepro. Having lube blown back is self-limiting once the upper dries out.

As always, YMMV.

Also FWIW, the only reason I'd want to get a piston upper such as the Leitner-Wise is to address these issues on a suppressed AR15.