Daryl:
Not too many Sniders actually have a 'normal' .585" groove diameter. My 3-bander is .598, and would digest .600 RBs happily if the cartridge neck still had clearance (it doesn't, and there lies the problem with most original Sniders).

Snider bores must be slugged, and then the real fun begins trying to fit a groove-diameter projectile in the case neck in such a way that it will chamber with safe clearance for neck expansion when fired. The Brits settled on undersized hollow-base projectiles with all manner of expander-plugs fitted, a poor solution accuracy-wise. The guys over on the MH forums load the Coyote heeled bullet (like a .22 rimfire), which appears to be the best solution short of opening up the chamber.

The other solution is to load the ball into the chamber first, followed by a shortened case full of powder closed with a wad (essentially a 'blank').

Hope this doesn't take us too far off topic....