9.3x57- you beat me to it. The #4 will also handle any pressure developed by the .458 WM without even snivelling(55,000PSI, I believe).
; We used the #4's re-barreled and chambered to the .308 WInchester (7.62x51 = T-56, I believe)- Anyway, the rifles worked just fine with 60,000PSI + loads, so a mere 50,000 to 55,000 should be OK. Nowadays, some clubs show a goodly number chambered for the .223. Interestingly enough, the standard extractor will handle almost any rim size, including the .22 hornet, without modification.
: The action and magazine will also take a .45/90 case, 2.4" long, and at 50,000 psi will deliver about 2,300fps with 400gr. softs or solids. Using 450gr. softs or solids, the velocities should be in the 2,200fps range. This case is a bit easier on bolt thrust than more tapered designs as well. Having a .505" head diameter makes for slightly less taper than the .458 Mag's .513" head. Modern brass is plenty strong enough for this chambering. I suppose it could be looked at as a poor man's 'African' or 'Alaskan' rifle, considering it's ballistics alone.
; I think it'd be great with a .50 2-1/2" case. Delrin liners can be made and screwed to the mag walls for straight line feeding. A 520gr. Cast bulet at 2,000fps to 2,100fps sounds kinda kinky.
; I have a #4 that I rechambered for the .312 Express - a few years before I found Ken Waters had already chambered and named that one. It uses a .350 Rem. mag. case necked for .312 bullets and does 2,960fps quite easily with 180's.
; The Enfields are very fast actions and it only takes a few hours of practise to become proficient as speed shooting with one.
: The Germans thought the Brits all had semiautos in the first war, due to the fast firing of their #3's.