Are you have to do this with 2 or 3 rounds still in the magazine?
So you fire a round, bolt cycles, and stays locked back on a full or partial magazine? I would look at the bolt catch\magazine first, if this is the case. JMHO
And when my DPMS Oracle was brand new, it made a bunch of brass glitter.
Dang nice feed ramps on that barrel!
Mobil1 full synthetic is your best friend and run it WET!