I would not worry about any PRB " skipping " in shallow rifling. If the ball is made of soft lead, its going to expand on firing, to force the patching into the grooves, and that will transfer the rifling's spin to the ball quite nicely.
Many of the old complaints about shooting RB in shallow rifled barrel came from people who didn't measure the bore of the gun before buying a mold, or balls for it, and often were using balls that were way undersized for it. Then you also had complaints, when the real cause of inaccuacy was blown patches, or burned patches, the wrong powder charges, etc. People just thought there was some " standard " powder charge and ball to use in all the guns, and didn't know how to, or that it was important to bench the gun and work up a load for that particular gun. Then, later, we started seeing problems with the bedding of the tang and barrels in the stocks, so that no matter how good a load they had, shooters still had shots all over the place because the barrel could shift in the stock.
If you go to the re-enactments held particularly on the East coast, where these type of Military reproductions are often used, the dealers on commercial row often include gunsmith to specialize in accurizing these kinds of guns. Some of the bores are so bad they need liners to make them shoot right. Most need to be bedded properly. Some need different sights than what comes from overseas, both to make them more accurate representations of originals, but also to help the shooter shoot them more accurately! And, of course, many need action and trigger work done so you don't bruise your thumb cocking, or your trigger finger firing the gun. There are other " Tricks of the trade" you can learn by hanging out around the right people! Some of them are even members here.
