looking for pistol
Thats a tall request. There is no ready made revolver that will go with a 50 cal rifle. There's no doubt that a revolver is fun to shoot, but it may well not the rifle. There are a number of traditional and non traditional design pistols out there. Currently cap and ball revolvers are not legal for hunting in seveal states. so Check your state. In PA a muzzleloader pistol must by 50 cal or over for deer, or 40 cal and under for small game.
If you want to hunt with it check with your state's hunting agency.
There are traditional side lock pistols in 50 cal, both flint and perc, and a very few models of more modern design pistols in 50 cal. Some models, though manufactured and listed on web sites are hard to find in reality.
See if you can get acquainted with some folks in your area who shoot such creatures and ask them to show you the advantages and disadvantages of the different styles.
Lastly, with 50 states and several territories, all having their own handgun laws, check to see if you need any kind of carry permit. Here in PA, a replica of a muzzleloader requires no permit to transport it in an automobile, but does require a permit to carry it concealed. Concealed includes stuck in your belt under your hunting jacket. or even in a belt holster, under your hunting coat. If it is carryed fully open for all to see, then no permit needed. Stupid! Every state has their own quirks, check yours.
