You need to do some homework I think. Determine your groove diameter of the barrel. Pound a pure lead ball into your lubed muzzle, withdraw it with a ball puller or a dead center sheet metal screw. Carefully measure the result. Mold: Don't go by the numbers, cast a bullet with your mold of a soft alloy, pure lead and 20 to 1 tin or wheelweight with a little tin. Compare the measurements. You want to be as close to groove diameter as you can get and still start the bullet in the muzzle. In the perfect world you would build a false muzzle to start your bullet.
Reliance on an evenly expanding skirt on a sloppy fitting bullet is recipe for disappointment. They used to sell bullets specifically for your type gun, Buffalo Ball-ets(great) and the TC, R.E.A.L(good) bullet. If you do this properly, the only limits to accuracy will be your sights.