I just bought a new Rock River upper and tried 2 different lowers and 2 different bolt carrier groups and still get light primer strikes everytime.The firing pin makes just a very light dent in the primer,but no fire,I tried different mags also,and the exact same ammo works in my other ar-15.I wonder if it is the headspace is out of spec? Any ideals? I'd hate to send it back in for repair but If I have too I will.Please advise,Thank you.
Did the upper come with its own bolt or are you using old bolts in the BCG's? New barrel should get a new bolt.
Take a bolt out of the BGC and make sure it fits correctly in the barrel extension.
I assume the bolt is closing completely when you cycle the action?? A tweaked gas tube might keep it from closing up fully. Does the BCG move freely in the upper when the upper is open or removed from the lower? Can you make the bolt lock in battery by hand in the open upper?