If your rifle is a Henry Patent Falling Block, it will almost certainly have Henry rifling, in which case IMO, you would be best advised to use correctly sized paper-patched cast lead projectiles. Jacketed pills can work in Henry rifling, but you have to be very carefull what you use, particularly in .450 calibre, since a lot of pills in that size are very hard, being intended for .458 Win. Mag.

As " kamilaroi" says, get a copy Graeme Wright's book, it takes the mystery out of all this.