go with a 45-70 bfr from magnum research , you can make load to achieve 454 or 460 velocity , or loaded up to greater velocity than the 500 s&w ,
Ammo are easy to find , the revolver are about the same weight of a 500 s&w or raging bull . I have one with 7.5 inch barrel and hell of a gun .
shooting at 100 yards is easy with that thing . the grip are crap , but with a wooden or rubber one are great , is just to not take grip with checkering or something non slip surface , because your's hand will hurt a lots , first 10 shots with this 5 shots my hand feel the pain , skin and flesh are red , and my thumb take all the recoil because the revolver don't slip and absorb the recoil , after that i shot many time with leather gloves and is a pleasure , don't take shooting glove because my rip in palm ..... leather glove without finger is best , and change the grips sooner you can to much enjoye shooting with that beast