Martin - the 'point-blank' sighting for very close or charging game, according to Forsyth, was taken down the rib. This pertained to muzzleloading double rifles. Since your double Snider is chambered for a fairly early ctg., it-too might have been sighted that way.
; Too - with it's 500gr.+ bullet of large diameter and relatively small powder charge, it's trajectory will be around 10" for 100 yards. This may be why the first blade is set so high. It therefore is possible that a sighting taken over the sight's lump, might give close to perfect bullet placement at 25 yards or closer. You will have to try it out to see whwere it shoots and with what load.
: Paper patching is sometimes a useful method of making an easily aquired mould work for you in a slightly oversize bore. Of course, different thicknesses of paper are available with the standard double wrapp. As long as the slant of the paper is different than the rate of twist, it should work. Butternick Notions patterns runs very thin, with various weights of printing paper running thicker, of course.
: BTW- lubed wonderwads, with a thin tablet-backing card to protect the powder from the lube, work well in most ctg. guns, accuracy wise. With a paper patched bullet, you may also need a lube wad, but eperimentation will show what's needed. Walter's vegetable wads have successfully been used by many shooters now, and they also are available from www.trackofthewolf.com in appropriate sizes - maybe, depending on your bores, of course.
; Good to hear you're not getting bullet migration in the .58. It's the first shot from a clean bore that usually causes movement in th eother bore as fouling then helps hold it against the powder. With proper engraving in the lands, the bullets should hold at any time. A friend of mine has the same gun, and shoots patched round balls in it with healthy powder charges. He re-crowned the muzzles as when purchased, they were rather sharply chamfered and didn't allow loading a tight enough combination. Emery cloth underneath the thumb rotating the barrels frequently, works wonders on too-sharp crowns.
; Good luck and keep us posted on the Snider's shooting.