Both the H&R Handi 45-70 22" barrel and Buffalo Classic 32" barrel are 1:20" which in the 45-70 is good for 1000yd shooting with 500gr bullets, there have been several discussions on converting them to muzzleloaders in the H&R Centerfire forum over the last few years, but the current production barrels have rather shallow rifling which wouldn't be the best. Older Shikari barrels had Ballard cut rifling which would make a better muzzleloader IMO.
Tim