Guys, my AR has been acting a little strange.  On 2 occasions today at the range, the bolt will lock almost all the way forward, i pull the trigger and only a click of the firing pin going forward.  I try to open the bolt with the charging handle and its stuck.  I cant move it with my hands, so i took a block of wood and had to tap the left side of the charging handle for it to come back and eject the unfired round.  Any idea on what might be causing this?  Everything is DPMS, LPK, upper, bolt, bolt carrier and barrel.  I was using Federal red box, 55gr fmjbt.

Other then that, it works like a charm and is accurate everytime.

Was the headspace checked with a go gage?