That is a project I'd be interested in the outcome of. The rim of the biggest 50 may cause problems for the No.1. They dies are available from RCBS, but are pricey. the original load with the 750 grain bullet and 140 grains of black(or smokeless equivilent) will certainly let you know the rifle went off. I would go with a tapered octogon barrel and to help with the balance of the rifle, I'd opt for a 30-32 incher. Remember the barrel may seem large but that's a really big hole thru the middle.. check the weight.. Stock it like an old express rifle but a shade straighter. Shotgun butt, steel(?) horn tip and cap?? I've been looking at one of these but can convince myself.. If I build one it would most likely be a 40-100. Plenty of horsepower and the lighter bullets make it a bit easier on the shoulder. This might be the platform that cries for a Keplinger single set trigger too!