Conicals??

The tough part is finding a design that works for your piece if you do not have the ability to fit the bullet to the barrel. Lee REALs are a partial fix to that problem in the they add a few thousandths to the workable range in bore sizes. Another way to approach the problem is to have a bullet that engraves on the rifling as does a maxi and also has a hollow base properly designed for heavy powder charges, thus providing an even greater spread of bore diameters that it can work with.

There's lots of ways to skin that cat. A rather brilliant design appeared a while back with a patched round ball for a tail end and a maxi ball front end.