Guys, I have a Beaumont-Vitali in 11X52 on the way, and it has a 1:29 twist barrel, I believe. I haven't Greenhilled it, but it is still a faster twist than the Martini-Henry with its 1:33. Question is, has anyone had any experience with cast slugs over 400 grains in .458 in a slower-twist BPCR barrel? I have heard the Beaumonts typically shoot the Lee 405-grain hollow-base over BP very respectably, and if so, the Lyman 457193 ought to shoot reasonably well, too.

I shoot my MH 577/450 with a 500gn .462 cast projectile and 90gn FFG.
I have shot a 10 shot group over the bench at 50m of 1.25" with this BP load.
I also shoot a smokeless load of 40gn IMR3031 with the same bullet out to 300m in our Service Rifle competition.

.......Bill in Oregon, I think you're mistaken on the M-H twist there ole pard. My MkIV 577-450 is a 22" twist. The .444 Marlin is a 32" twist and it'll handle a 350 gr bullet, but at a higher velocity then your Vitali. I'd think, just off the top of my head that you're looking at a 300 gr bullet or so?

.........Buckshot