As a rule, the longer the bullet, the faster it must be spun to remain stable. If you are going to use the 155 to 195-grain bullets, then a 1/32 to 1/28 twist is about right. I use a 1/20" twist to shoot .45/70 bullets in a .45 caliber muzzleloader. These bullets run from 345 grains to 400 grains or more. I size them to .451", and they are a tight but sliding fit in my bore. I also have a .45 and a .50 cal. with slow twists, made for round balls. But, the .45 will shoot short bullets (for example, the Buffalo Bullet or Maxi-ball) up to 275 grains, and the .50 will shoot 370 grain Maxi balls with acceptable hunting accuracy to 100 more more yards. Both of these barrels are slower than 1/60". In addition, I have a 1/60" twist /58 that shoots the Lyman 57730, a 570-grain Minie ball, to the same point of impact at 100 yards as the .570 round ball, both bullets using 120 grains of powder. However, if I were purchasing a rifle today for use with conicals or sabots, I would buy one with a twist of at least 1/32", or faster!!For shooting plain round balls or short Minie balls, I would get a 1/66" (or 1/72", if a .58 caliber).

Keep yore powder dry!!