The COP .357 is an American 4-shot Derringer-type pistol chambered for .357 Magnum.

The double-action weapon is about twice as wide and substantially heavier than the typical .25 automatic pistol, though its relatively compact size and powerful cartridge made it an option for a defensive weapon or a police backup gun.

It uses an internal hammer, which is activated by depressing the trigger to hit a ratcheting/rotating striker that in turn strikes one firing pin at a time.

The COP .357 operates similarly to the Sharps Derringer of the 1850s, in that it uses the ratcheting/rotating striker, which is completely internal, to fire each chamber in sequence.

[1] A smaller caliber version, the "MINI COP" was also manufactured in .22 Magnum.