This is the Bond Arms Rowdy, a very solid, very well-made compact
derringer chambered for both 45 Long Colt and 410 shotgun shells.
Bond Arms derringers are unique in that the barrels are
interchangeable, and are the “caliber-specific” components
of the firearm. This model features 3-inch barrels.
Specifications:

Compatible with all standard Bond Arms barrels
Automatic spent casing extractor
Patented rebounding hammer
Retracting firing pins
Spring-loaded, cammed locking lever