Well cptnron, I suspect it's a matter of perspective from the manufacturers' standpoint. They would envision an Encore muzzle loader as a modern scope sighted sabot shooting gun. That automatically sets the bar at .50 caliber. Fifty-four doesn't really make much sense for saboted bullets. Why shoot a .45 caliber bullet in a 54/45 sabot when you can do it more efficiently in a 50/45 sabot?

The .54 is a dandy round ball caliber. But it really wants a slower twist than the typical 1:28 sabot twist to perform at its best. I may be wrong, but I suspect demand for a ball shooting Encore barrel would be too low to justify production.