Shot my Marlin Cowboy today with with my PC LBT 260gr GC bullet, sized at .380. BHN 10.5 from scrap WW & PC. As long as I stayed at 1400 fps ( chrono said 1406 ) it shot great ( 100 yd target shown ). Used IMR- 4198 powder. If I added just 1 gr more powder the group grew to over 2"with an occasion flier, way out. The same bullet cast from my BHN 16 alloy, sized & lube with LBT soft blue will shoot this same size ( small group ) at 1688 fps. So why? It was my assumption PC on a bullet would allow a higher velocity with the softer alloy. Does the PC bullet also have to be of the harder alloy to achieve accuracy at the higher velocity ? This Marlin has what Marlin calls the " Ballard Deep Grove " rifling. Not Micro Grove. Picture of the two bullets, one with PC, the other with traditional lube. What am I missing here.