The bore on my C sharp slugs out at .4495/.450. I have a supply of Seth Cole 55 which mics at .0016 to .0018. depending on humidity I guess. I want to try a .443 slick but only seem to find .442/.444 at BACO. I will get a custom mold once I find a good candidate. It's a 34" BBL 1x18 twist 45-2 7/8. The other I'm concerned with, since its a heavy 550gr slug, is alloy. would 20-1 be better than pure lead as far as bullet distortion.