I dont shoot a scoped ar, and need to get a iron sight entry . So this is speculation on my part, are you adjusting focus and paralex while shooting the group? I would load 12 with that same load ,1st into the berm , shoot 10 , then unload the 12th, might have something to do with decreasing mag/ rd pressure on the bottom of your bolt causing some type tilting with the bullet in the leade/ throat however small it might be , i would try the 12 shot mag deal see if those middle 10 group.
