A Minie will work with a 1/66 twist ok. My Richmond R-M has a 1/48 six groove barrel. The problem is the deep grooves in a round ball gun. The Minie was designed for use in a barrel with progressive depth rifling, deep at the breech and very shallow at the muzzle. Also very wide lands and grooves. In the case of Springfield muskets, that would be 3 grooves, .015" at the breech tapering to .005" at the muzzle. Enfields were similar, though some contractor arms such as Pryse & Redmond used 5 groove barrels. What it boils down to is the rifling needs to be wide enough and shallow enough to allow the bullet to obdurate or upset into the grooves to both engage the rifling and seal off the gases. Deep narrow grooves won't let that happen, especially if you use the powder charge the Minie was designed for or less. An example would be my barrel. With a fairly fast twist and twice the grooves of the original, my Richmond does best with 50 grs. of powder rather than the service charge of 60 grs. The big advantage of the Minie is the speed of reloading. If properly lubed, quite a few rounds can be loaded quickly without wiping. Also, you get much more bullet weight, but that comes with a price. Velocity drops greatly and you'll have to change sights. For hunting you'd be just as well off staying with the round ball. But, I'm not one to say you can't experiment. If you have a barrel with shallow grooves, you might have something that'll work.