350 gr. is actually light for a .510 cal.... A roundball in that caliber is almost 200 gr.... Arsenal have moulds for 310 gr., 365 gr. and 400 gr.... Accurate have 30 designs between 300 gr. and 385 gr.... You will have to determine the groove diameter of the barrel to know what to get....Bob
0.495" groove diameter?.... What a weird size....Bob