I've been grabbing a box here and there of BiMart's 5.56 ammo when it goes on sale & finally shot a few mags of it yesterday. 3 out of 3 times, the bolt didn't lock back on empty. This usually happens when I use PMC, but didn't expect this on what I thought is a 'hotter' load. Wolf, Tula, custom 69 gr reloads, gunshow 55gr reloads will all lock back my bolt on empty, but this stuff didn't. Its not the mag, either. I do have a heavier buffer (H2) installed. I could go back to the H buffer, but would rather not. I've heard anecdotally the BiMart stuff is 2nds, could it be these are not loaded to spec? The fireball from my barrel says otherwise tho...(10.5" SBR). TIA.