This is a Bond Arms known as the Cowboy Defender chambered in 357 Magnum, model CD357MAG.
Bond Arms Derringers come standard with a rebounding and locking hammer" which is a first for derringers. The hammer automatically jumps back and locks into a half-cocked position for safety. A Simple Barrel-locking mechanism that is spring loaded allows easy opening and closing of the barrels for quick reloading and cleaning.
Features:
Heavy-Duty Stainless Steel
Spring Loaded Barrel-Locking Mechanism
Precision Machined Parts for Consistent Fit