I've noticed a few comments about 9mm AR's blowing debris and gas back into the shooters face, and I was wondering if that is a common problem, or one more related to a particular brand of AR or ammunition?   I'm trying to narrow down my choices for a new 9mm.

My Oly-style upper has had a couple thousand rounds fired through it by several different people, all gun guys and all FA.  No one (including me) has ever said anything about gas or debris or anything else coming back into their face.

The only time we complain about gas is when one of the guys has a bean burrito for lunch

no gas or stuff in the face for me either.

Most likely it is the southpaws that have a problem with blow back. Me, I do not have any problems.

Suppressor  will add gas back in the upper, I'm rihgt hand, and it bothered me,  7oz buffer slowed that problem.

Thou shalt wear thy balistic eye wear whenst shooting!!

Thanks for the feedback.   I had considered the "port side" issue, but this is all a new area for me.  The goal is to (someday) go SBR and add a can for that extra touch of fun!

I'm thinking that you might get a gas discharge from the chamber if you run to light of buffer or spring. I have recently purchased an Oly 9mm upper. I was itching to give it a try and I didn't have a heavier buffer that the stock M4 carbine one. So I did and what I and a buddy noticed is a bit of flame form the chamber area because the bolt was coming back before the powder was completly burnt up. I would feel a few piece of something hit my cheak every once in a while also.

This last night (New Years Eve) my buddy and myself decided to go up into the woods and try a few firearms to see the difference in muzzle flash. I also wanted to try out my new Hahn mag block to see if the Stem mags would work. My buddy also lent me an  MGI RRB buffer to try it out. All I can say is what a difference it made in recoil and no noticable flames out of the chamber area. Before the recoil with the stock spring and buffer were more than my M4 clone. With the different buffer I would say that it is reduced to 20% of what it was. This is not reduced by 20% but down to about 1/5th or the felt recoil. Also, there were no failures with this setup, although limited testing.

Right now buying one of these buffers is not in the cards, but next outing I will have a heavier spring and 9mm buffer to try. I don't know which buffer yet, but it will be somewhere around the 5.X ounce.

I also wanted to mention that I have a different stock on the gun right now. I used to have a standard  M4 stock on it. I now have one of the short ACE stocks on it. Someday when it will end up being and SBR wih can.

Nox

If it's problems from gas coming out into the face of a southpaw, try a gas deflector. I'm a lefty, and it solved 100% of my problems.

Gas Deflector
Gas Deflector Spring
Ejection Port Cover Assembly

I've been shooting a Colt upper for many years (left-handed) and have never had a problem with gas unless I am running a suppressor on the gun.  At that, the gas is not a problem at all.  On the other hand, the same gun in .223 with a suppressor was obnoxious gas-wise until I plugged the gap between the charging handle and the receiver with some silicone sealer.

Makes me wish I hadn't wasted money on the PRI so-called "Gas Buster" charging handle, which didn't solve the problem.  It helped, but the gas still got through.

I have an Olympic 9mm AR and have not experience any blowback while firing.  I am using a RRA 9mm buffer and have fired both right and left handed.

I have an Oly 9mm upper with the shell deflector, but not a gas deflector. I'm left handed, and I had a lot of gas and junk in my face.

I did what 'NAM' did, and installed a gas deflector and now it's not a problem. Does look kind of funny with the shell and gas deflector on it.

Quoted: If it's problems from gas coming out into the face of a southpaw, try a gas deflector. I'm a lefty, and it solved 100% of my problems. Gas Deflector Gas Deflector Spring Ejection Port Cover Assembly tinypic.com/jibyag.gif

Ditto

None noticed at all.  About 10K rounds last year.