TH44
you have a wonderful rifle the matey - it's a corker! Will make a wonderful BP Express regardless.
What is the actual 'Proof' load for this old girl?

I don't know the comparative 'strength' of actions (Rolling block Vs Martini) but if this round fitted into an "WR improved Martini", really a normal large Martini, they could certainly take a fair old load of BP behind them - refer this old thread!
http://forums.nitroexpress.com/showflat....SID=#Post258697

I guess the Martini Henry 577/450 load was restricted the 85gn service load, but a hunting rifle is shot a hell of a lot less than a battle rifle & hence a greater charge & recoil?