Me, I prefer an RPG or something to that affect.
A gun made in the 1800’s would likely be too valuable and too weak to be used with modern ammo-unless the ammo was purposely downgraded. With that said, there are lots of modern-day copies of old timey revolvers made. Uberti, an Italian firearm maker comes to mind and their revolvers are built to shoot modern day ammo. The cowboy action shooting hobby has brought a lot of this about.
Someone above mentioned the gun involved was a .44 caliber revolver. That is a hefty, large diameter projectile and it takes a lot of force-i.e. gunpowder, to fire it out of the barrel at high enough velocity to penetrate a body. But until all the facts are in, it’s just speculation.
Me? I’m more of a Claymore fan, myself. ;)