Last weekend, I actually accuracy tested my Geissele 14.5 URGI factory upper and an upper that I built using a Daniel Defense 14.5" SOCOM profile barrel. Ammo used was 77 grain AAC Sierra Match Kings and AAC 75 grain BTHP. I shot several 5 shot groups with both rifles and both types of ammo. Overall, the 77 SMK shot tighter groups in both rifles. More @Wikipedia
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