Hey there North-Woods -- I've had some pretty good results with a 120 grain Missouri Bullet Company (.com) cast bullet and from 4.5 to 5 grains of Unique. My newer Marlins seem to prefer the lighter loads and the old guy likes 5 grains of Unique. The Speer 115 grain 327 Federal Magnum jacketed hollow points work well too. They are .312" in diameter and pack a pretty good punch over 9.5 grains of 2400. Best regards. Wind