Lyman makes a .69 calibre Minnie Ball (hollow base). This 730gr. pure lead projectile was the one used in the .69 calibre rifled muskets in the 50's and 60's. The standard military charge was 70gr. as opposed to the 60gr. charge used in the .58's and .54's with their Minnie Ball loads. The .69's, which were merely muskets that had been rifled to the .58 Minnie Rifle pattern, ie: progressive depth from .003" at the muzzle to .011" deep at the breech. The bores remained consistant at .690".

It is possible that Dixie Gun Works has something as well.

The Lyman Minnie, the original pattern slug will either make you cringe or smile. It is only 30gr. heavier than a pure lead 10 bore round ball.