The common denominator with the working lower was the MGI Buffer. New springs and yet another round of cleaning the carrier and fresh lube did nothing for the bursting.

Put the upper on my RRA with the MGI, no burst. Insert the MGI in the new Stag lower, no burst.

300 rounds later, no more problems.

I was running 'H' buffers in the Cav. Mk. II. and the Stag lower. I guess it just needed more weight to slow the cycle rate.

Also notice that the gas deflector is already chewed up from brass. This never happened with my last 9mm at all. Pic of the deflector later today.







Yes, I've read the FAQ and other threads with this problem but I think in this case, it's an upper problem.

9mm Olympic upper. Fresh and clean.

Lowers used were:

Cav. Arms Mk. II
RRA with 6 position and an MGI buffer
Brand new Stag complete lower

With the Cav, after about 75 rounds it would start to burst.  Since I bought this lower used, I thought the LPK may be worn. So I stopped and put the upper on my RRA lower.

RRA lower and the 9mm upper run fine. Also using reduced power trigger springs in this one.

Brand new Stag lower...
First trigger pull, bang, second pull created a nice brass rainbow.  Ammo being used was WWB.

Had the range officer there in about  :30, and local PD just happened to be there running drills.

First thought is slam-fire from a stuck firing pin. Pulled the bolt,  firing pin is not stuck, and firing pin return spring is strong. Carrier moves freely.

All lowers pass the disconnect test and don't allow the hammer to fall while holding the trigger back and hand cycling the bolt.  All lowers work fine with my 5.56 uppers.

I'm stumped, and open to suggestions before I take it to a smith.

tvone

What type of ammo were you useing. I have had low power rounds in my uzi carb.cycle the action just enough to go auto.

I had a problem with my OLY. After I had run 1k+ my gun started to double, even fired some 3 round bursts. When I emptied the next unfired round in the chamber there was a firing pin impression on the primer it was a light impression. When I 1st experienced this I swapped to a different lower it ran ok for about 250 rounds and the same thing happened again. I was using Win White box for ammo. However I cleanedup my bolt and made sure the firing pin was free, oiled it. After that I have not experienced any issue in the last 9k I ran through the gun.

That deflector is really beatup! Glad you got it fixed!!!

I'M SORRY GUYS...BUT OLY SUCKS!
I have had a 10mm go full on me, and my Lt's .40 does it all the time. Their QC blows. I will carry an SKS on duty before any OLY product.

I can't fault Oly with this. It was not a complete gun and every firearm has nuances. As far as the workmanship on the upper, everything is in order. It's a good looking upper. No marks, blemishes, scratches, etc.

If I was buying a complete firearm, and it did this, then I would have reason to gripe.  

Pistol caliber AR's are toys.  They are a ton of fun. I can shoot indoors, and ammo is cheap.

If I need a serious weapon for serious work, 5.56 is in my hand. I wouldn't even think about picking this up for protection if I had a choice. If you're a LEO, and have an AR, at least carry a 5.56. Anything less is just a long barrelled pistol.

Why is that huge deflector on an Oly?  Is it an old one?  I have two and neither have that huge thing.  That may be your problem.

Quoted: Why is that huge deflector on an Oly?  Is it an old one?  I have two and neither have that huge thing.  That may be your problem.

I think that's actually a gas deflector.


Vulcan94

It is right by the ejection port, colt style.  Do these belong on an Oly?  Anybody else have one?