I put about 10 rounds through my AR (dpms upper/plum crazy lower) and on the 11th shot the firing pin hit the primer but nothing happened, I ejected the shell and tried another with no luck. I pulled the bolt and wiped it down but still no luck. Each primer had a dimple from where the firing pin was striking? I plan on cleaning the bolt really well tonight but do you guys have any other suggestions of what is causing this? Thanks