Some of you may have seen my other thread. It's a long saga that has finally led me to having a Ruger No. 1 in .458 WinMag at my gunsmith being rechambered to .450 Rigby. Lots of stuff happened to get here too long and convoluted to relate except to say I want to take my first Cape buff in two years. I want to do it with a single shot. I am a very minor Ruger collector and FedEx destroyed the collector value of this rifle before I ever took possession. Why a .450 Rigby? It is easier to load the rifle fast, under pressure, with bottle neck than straight wall cartridges. It operates at lower pressures than the Lott. I don't need to use a filler in the case as with .450 NE cartridge. Ruger has never produced a factory .450 Rigby. And the point of this thread...the cartridge has the capability to deliver 500 grains at 2250 well under max. Those loads are straight forward and easy to find. It should also be able to shoot 300-350 TTSX or TSX at 2650 to 2750 making it good for N. American hunting or larger plains game. I'd like to gain experience with the rifle using the lighter bullet loads before the buffalo hunt. Can any of you help with a starting place, advice, or pointers on how to safely arrive at the data I need? The rifle won't be back to me for a few months so I'm just collecting data and components at the moment. Thanks!