Be hard not to try a 55 grain Gameking BTSP for accuracy.
50 or 55 BT, BK or any boat tail, and yes the top is where the accuracy lives. I am guessing the pressure problem is due to the flat base
was told by Sierra that the 53 match flat base has more bearing surface than the 52 SMK which was causing a 100 + FPS drop in velocity for the same load. This may also explain the pressure at a full grain under book max.
