I think the twist of 20" or 22" is just fine for stout jacketed ammo loads in bullet weights up to 500gr. For shooting the long 550 to 600gr. cast bullets, an 18" or faster twist may be necessary.
: I feel there is a trend today towards overly rapid twists - even as fast as 12" in .50cal, when 24" is all that's really needed to 600gr. weight of bullet.
; I think that rapid twists today are responsible for the tumbling of solids when penetrating through an animal, but have no real proof of that. In my theory, the bullet starts out overstabilized, and the attendant slight yaw promotes tumbing whem striking the animal close in. The fast twists may be necessary for very long range target shooting beyond 400yd., but that's a moot "Plus" for a big game rifle.
: Please correct me if I'm wrong on this theory.
: Unfortunetly, the Ruger .45/70 barrels are very light-weight. I would re-barrel to a heavier weight barrel, 25" long, then chamber for the 3 1/4" Sharps case - .450 Nitro load data would probably duplicate in the RCBS or Bell case.
: I have easily run 500gr. bullets to 2,000fps in an Italian rolling block in .45 3-1/4" brass.
: Brass is available rather reasonably priced from www.trackofthewolf.com