It shouldn't be a smoothbore, maybe the muzzle was coned. I've got a .54 CVA barrel on my Investarms and it shoots very well. Yes it can be done but takes some doing.
Even has the patent breech. It depends on the twist whether it's strictly a round ball barrel. It should be either a 1:48 which will handle PRB's or conicals very well or a 1:66 which will handle PRB's excellently but won't do well at all with conicals.