ok, looking for theories as to why some barrels like certain bullets, while others don't. personally, i've had 4 AR barrels over time. the last two were JP 18", same contour. on the first, it loved 77's. on my newest one, it can't hold a group with anything above 69's. both loved 55 NBT's. go figure. IAC, im curious what theories there might be as to the variances.