I have had many conversations with Doc White as my Optima V2 pistol has been in his queue waiting for its turn to come up.
One of those conversations was about patched ball shooting in fast twist barrels, which lest face it are mostly on inline rifles.
ALL fast twist barrels can shoot a patched ball. The peculiarities of the individual barrel, and the rate of twist, are going to determine the maximum amount of powder charge that the patch/ball will handle.
Almost always, it will require a VERY TIGHTLY fitting patch & ball combination in order to make it work with the shallow grooves in most inline rifles. That's why Thompson/Center rifles back in the day got such a bad reputation for shooting patched balls. The depth of the grooves in T/C guns had always been 0.005" deep, just 0.001"-0.002" deeper than any modern inline rifle sold in the past 50 years. Shallow grooves don't mix well, USUALLY, with a loose patch/ball combo.
Shallow grooves and fast twists usually results in a mild powder charge that limits the range, and often eliminates a large bore rifle from being a big game gun with patched balls.
20-40 grain black powder charges aren't big game charges, but are more than adequate for small game hunting, and keeping one's marksmanship up without spending a lot of money. Theoretically, such charges WOULD kill a deer ethically, but ONLY at VERY SHORT DISTANCES. Say, 25-30 yards and under. And, should probably be chronographed to be checked for muzzle velocity & muzzle energy before deer hunting with such a light charge.
IF HOWEVER, you want to really hunt big game with an inline using full loads with a patched ball, then a barrel with proper depth rifling for patched balls, and a good rate of twist is necessary. In .54 caliber, I don't think one can go wrong with the old standby, 1:48" twist, unless you have a case of magnumitis, then a 1:72" twist would be in order.