If you already have a .50 cal, maybe a .500 S&W X-frame, .500 JRH BFR, or a .500 Wyoming Express Freedom Arms 83. Then you can just stick to a single diameter for your hand cannons. If you already are not there, once you get heavily invested in reloading and casting, at some point logistical simplification becomes preferential. If I were gonna do everything over again, I'd probably stick to 2 handgun rounds and maybe 3 rifle rounds for all my needs. If that line of logic doesn't appeal to you, a Ruger Alaskan .454 is SUPER fun.