So I bought an AR15 from a buddy. its a stock DPMS lower with an A2 fixed stock, with a Bushmaster M4 upper. First thing I did was to add all the usual magpul furniture. Went and got a collapsible magpul stock, and buffer tube kit (milspec)to convert from fixed to collapsible. I took the rifle out a couple times to shoot, but every time it would either fail to eject, fail to chamber the next round or the bolt would lock back. So I took it down to Curts and had them go through the upper assembly and check out the gas system, and to remove/swap the triangle sight for a railed gas block. I was hoping that the gas system was to blame for my problems. So I got my upper back and took it out last weekend to test out again, and every time it would fail to eject the round, and from what my buddy could see he thought it looked like the bolt wasn't cycling all the way back. So my question is, what problem could I still be having??? Is there something different in a commercial spec vs mil spec buffer tube setup that could be causing this or do I have some other problem that I'm not aware of. Thanks!!!