My 58 cal shoots the 525 gr great plains conical with a 100 gr. of 777 real well but it is a 1:48 twist. My 1:70 twist won't stabilize the conical , they shoot strictly round ball. I have a few green Mountain barrels and i'm pretty sure the 58 cal is a 1:70 twist. I seriously doubt it will shoot that conical. Unless the twist is faster than what I think it is



+++++++++++++++++++++++++++++