A friend of mine bought a S&W AR and the fired cases bulge slightly, not much but enough to see it when you place them on a flat surface. The case head mics at .374 but then grow to .378, I thought maybe excessive headspace but I didn't see any growth in length so now I'm thinking maybe the chamber is every so slightly too large? The barrel is marked 5.56MM, it shoots well and is accurate I'm just concerned this will case premature brass wear for him since he wants to reload for it.