Hey
Grouse, which one of the FTX bullets were used? I suspect some of them are tougher than others.
I think
Lee may be on the right track with the Bushmaster bullet which is probably designed to operate at a little over 2000 fps muzzle velocity. I suspect the one designed for the 460 S&W would be the most appropriate for muzzle loader velocities, but a 200 grain .452 bullet is pretty short and fat and would probably be only a 100 yard bullet anyway. A regular old XTP is probably better.