Simple enough, the current star in this field is the Magnum Research BFR (Big Frame Revolver) you can get this little monstrosity in several calibers like .500 S&W, .475 Linebaugh, .45-70 Gov't, and .30-30 Winchester. For our purposes, the .45-70 is our go too for this.
Obviously, this'll be the heaviest revolver in game and it will hit with MASSIVE penetration (handgun bullets are designed so that penetration is the main factor in taking an animal down, a bullet from a revolver wouldn't mushroom correctly if the bullet is made the same as for a rifle) the sights will be a bit blocky just due to the size of the gun.
Ideally, this would come with a few changes to the .45-70 round and Coachmate (it has a rail just like the Moradi, why does it require a special scope?). The biggest change would be to the classes the gun covers, I'd personally rather see .45-70 cover 6 or 7 thru 9, the .30-30 already covers 2-6 (which makes no sense, should be 3-7 any day of the week). We have very few 7-9 calibers in game and almost none of them make sense. (.300, should be 4-9 based on the rabid fans I've met in Wyoming) and the .45-70 in game is LITERALLY modeled on the Guide Gun, popular in Alaska for hunting brown bear because of high penetration and knockdown power. It should rival the pen on the .470 (not exactly but close, like 75 or 85). For balance(?) make the ammo more expensive than .338 rounds and less than .470 rounds.