Get thee and thy rifle to a gunsmith at the soonest. Something is keeping your ammo from fully chambering. Or possibly a firing pin problem. Is it a slam fire, or did you pull the trigger and it went boom?
Be sure to bring your ammo with the rifle. I have shot thousands of Remington UMC out of my AR's with no problems. Maybe a bad lot of ammo. It has happened before..
Your problem can not be fixed over the internet. If you are close to Ft Wayne, I can look at it. Others on this board can look at it too. Just don't shoot it until it is diagnosed and fixed.
So ppl are blaming it on PMAGS now lol???
i'm not, but since i spend way too many hours on here and ar15 i tend to read alot. It isn't that people are blaming the mags, it's just that there is nowhere for the pressure to go when the ammo goes bad, except down the mag. Typically you will have a mag that kindof explodes, and you will have a f-up'd upper receiver and a bent BCG. I doesn't matter to me, i still shoot **** ammo and use pmags in all of my ar's.