The ultra-traditional thing to do would be to preserve the Henry rifling, regardless of the cartridge selected . My AH is a .450 Boxer-Henry Long (basically the same case), but has a 7-sided polygonal bore. Maybe you could do something with a 577/450 Martini-Henry barrel, putting in some sort of liner to fill in the void left by the 577/450 chamber, then re-chambering for an appropriate (and easier to use) cartridge. IMHO, if you try bore conservation, it will be a "lead bullet only" rifle.
Unless, of course, some present-day barrel maker is willing to reproduce the rifling. Even then, Henry rifling and jacketed bullets are probably not compatible.
Last edited by waterman; 07/07/14 09:17 PM.