Speer makes a 270 gr FP Gold Dot (.429) for the 444 Marlin that makes an excellent high(er) velocity muzzle loader bullet. At lower velocities I've had good accuracy from 44 cal bullets, but once I went much over 2200 fps in my Savage they began to open up. Even at that I had consistent 2-3 inch groups a 100 yds. At slower 1700-1900 fps they would stay around 1.5 inches. Never worse, never better.