I have aSystem One with both 50 and 54 barrels both 1-38 twist,they both do well with round ball at 90 gr of P,the 50 shoots tight groups with 180 and 200 gr 44cal in sabots and 230 gr XTP with 150 RS and the 54 shoots tight groups with 270 and 300 gr Widner 50 cal pistol bullets with 140 gr of RS they will also shoot ballet maxie hunter and maxie ball. The limitation seems to start at 250gr XTP which it will shoot well but the 50 wont shoot 300gr or above. Hope this helps. Lee