The COP .357 is quite robust in design and construction. It is made of solid stainless steel components. Cartridges are loaded into the four separate chambers by sliding a latch that "pops-up" the barrel for loading purposes, similar to top-break shotguns. Each of the four chambers has its own dedicated firing pin. 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. Older "pepperboxes" also used multiple barrels, but the barrels were the part that rotated. 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.^[2]

Two complaints about the COP .357 are that it is too heavy to be used as a backup gun, and that the trigger pull is too heavy for rapid fire, even heavier than most modern revolvers.^[2]

A smaller caliber version the "MINI COP" was also manufactured in .22 Magnum.^[2]

It was designed by Robert Hillberg, based on his earlier work on the Hillberg Insurgency Weapon. It was manufactured from 1983 to 1989 by the now defunct COP Inc. of California, US (COP stood for Compact Off-Duty Police). In 1990 it was manufactured by American Derringer for a short time.^[2]

• Derringer
• Heckler & Koch P11, a multi-barreled pistol that can be fired underwater
• Lancaster Pistol, another cartridge-firing break-action multi-barreled pistol used from the mid 19th century until World War I
• Mossberg Brownie

• Leon's Gun: Mother's Defender
• How a COP .357 Derringer works