I had a batch of Ammo Inc 223 that was all sorts of screwy, with the powder and primers so messed up that it had 2 of my ARs slam-firing. That's the only factory ammo I've ever had with pierced primers, but it gave a couple of 2 and 3-round full-auto bursts. Best I could tell, the powder was peaking the pressure way too high, way too close to the gas port - that flung the BCG back way too fast, and on the forward stroke the floating firing pin punched right through the primer. In 2 cases, the anvil of the primer flowed right into the bolt's firing-pin hole, keeping the casing from ejecting. At least part of the problem, I suspect, came from not using the thicker cups of magnum or AR-rated primers.