The Colt Model 1903 Pocket Hammerless is .32 ACP

.32 ACP

.32 ACP , also known as the .32 Automatic is a pistol cartridge. It is a semi-rimmed, straight-walled cartridge developed by firearms designer John Browning, initially for use in the FN M1900 semi-automatic pistol...

 caliber, self-loading, semi-automatic pistol designed by John Browning

John Browning

John Moses Browning , born in Ogden, Utah, was an American firearms designer who developed many varieties of military and civilian firearms, cartridges, and gun mechanisms, many of which are still in use around the world...

 and built by Colt

Colt's Manufacturing Company

Colt's Manufacturing Company is a United States firearms manufacturer, whose first predecessor corporation was founded in 1836 by Sam Colt. Colt is best known for the engineering, production, and marketing of firearms over the later half of the 19th and the 20th century...

 Patent Firearms Manufacturing Company of Hartford, Connecticut. The Colt Model 1908 Pocket Hammerless is a variant introduced five years later in .380 ACP

.380 ACP

The .380 ACP pistol cartridge is a rimless, straight-walled pistol cartridge developed by firearms designer John Browning. The cartridge headspaces on the mouth of the case. It was introduced in 1908 by Colt, and has been a popular self-defense cartridge ever since...

 caliber.

These pistols were popular civilian firearms for much of their life, and also served as United States General Officer pistols from the 1940s until their replacement by the M15 General Officers pistol in the 1970s.