NAME – 6.35×15.5mmSR

NAME (COMMON) – .25 ACP (Automatic Colt Pistol), 25 Auto

TYPE – Semi-rimmed centerfire

YEAR OF INTRODUCTION – 1906

COUNTRY OF ORIGIN – Belgium

CASE TYPE – Semi-rimmed straight

CARTRIDGE LENGTH – 23.1 mm (0.91 in)

CASING LENGTH – 15.7 mm (0.62 in)

CASE HEAD DIAMETER – 7 mm (0.277 in)

CASE RIM DIAMETER – 7.7 mm (0.298 in)

BULLET TYPE – Round-nosed, full metal jacket

BULLET DIAMETER – 6.38 mm (0.251 in)

BULLET WEIGHT – 3.24 g (50 grains)

POWDER WEIGHT – 0.08 g (1.2 grains)

CASING WEIGHT – 1.68 g (26 grains)

TOTAL ROUND WEIGHT – 4.99 g (77 grains)

MUZZLE VELOCITY – 250 m/s (820 fps)

NOMINAL BARREL LENGTH – 5.1 cm (2 in)

MUZZLE ENERGY – 101 j (75 ft/lb)

     This is the smallest centerfire round commonly encountered. Developed in Belgium by John Browning for his new pocket semiautomatic pistol. The 6.35×15.5mmSR (25 ACP) round was considered sufficient as a self-defense round in the early 1900s. The main appeal of the round was that it could be chambered in relatively small handguns that could be used to intimidate or wound, rather than outright kill, an attacker. For the era, even a small would could quickly become lethal due to infection. The semi-rimmed (SR) aspect of the round also allow it to be chambered in small revolvers. It has been considered a military cartridge only in that high-ranking officers, particularly in Europe, would carry small pistols chambered in the round solely for self-defense.