If you want to shoot roundball from a .54 caliber you need look no further then a Lyman Great Plains Rifle.
Midsouth Shooter's Supply has some excellent prices on them. They will sure get the job done. And an excellent choice picking the .54 over the .50. The only thing I do different is I shoot a .58 caliber with 1:70 twist in a Green Mountian Barrel. 100 grains of Goex FFg and a moosemilk patched roundball and nothing will stand in the way.....
D&R Sports also carry Lymans