The 45-70 twist rate is 1:20" as stated in the FAQ, chamber throats are short so loading long range bullets will cost you if shooting black powder, those that want to shoot black and long range usually have the throat deepening with a throating reamer. Shooting smokeless won't be a problem, though. Another option is to have it reamed to 45-90 or 45-120 or something in between as several members have done, mine was to 45-120. Best recommendation for bore dimensions is to slug the bore to find out what to size cast bullets to. Most shoot .459-.460" very welll.
Merry Christmas to you and yours!! :wink: