Fire and Maneuver

Doing a quick fire and maneuver drill, Cammed rifle is a Spikes Tactical Heavy Barrel, Piston Driven (Osprey Ops-416). Most of the AR mags used were US GI mags. Upon seating second US GI mag, the first round pops out thru the feed lips. Shooter observing the chamber during mag change notices the failure and dumps his rifle to the side to clear the malfunction. Continues to fire and maneuver to the objective..