Not to make light of your issue, but are you using the right ammo? No mention if your AR is chambered in 5.56mm or .223. There is a difference. 5.56mm will stick in a .223 chamber and my be causing your issues. The 5.56 is just ever so slightly larger, by thousands of an inch, but it does not fit a .223 chamber well is tolerances are tight.
so, to sum up
5.56mm will not work properly in a .223.
.223 will work properly in a 5.56mm.
I'm sure if this is not the problem, others more educated on this subject will steer you right.