Original John Browning semi-auto pistol cartridge for the Colt 1900 and Model 1902. Predecessor to the .38 Super — externally identical but loaded to lower pressure. Critical safety note: .38 ACP and .38 Super are dimensionally the same but .38 Super is loaded much hotter; .38 ACP pistols should not fire .38 Super.
Type: Pistol
Introduced: 1900, United States
Parent case: None
Standardization: SAAMI
Bullet diameter: 0.358" (9.09 mm)
Case length: 0.9" (22.86 mm)
Overall length: 1.28" (32.51 mm)
Max pressure: 26,500 PSI
Rim type: Semi-Rimmed
Primer: Small Pistol
Typical twist rate: 1:16
Muzzle velocity: 1040–1100 fps
Muzzle energy: 300–349 ft-lbs
Effective range: 50 yd
Common bullet weights: 125, 130 gr
Primary use: Military, Self Defense
Production status: Discontinued
Also known as: .38 Auto · .38 Automatic Colt Pistol · 9x23mmSR
History: Developed by John Browning for Colt's first semi-automatic pistols (Model 1900, 1902, 1903). The cartridge was the basis of early US military semi-auto trials before the .45 ACP was adopted. In 1929, Colt introduced the .38 Super as a higher-pressure version of the .38 ACP for the M1911 platform. The .38 ACP is now a collector cartridge associated with early Colt semi-automatics.
Notable firearms: Colt Model 1900, Colt Model 1902, Colt Model 1903
Military use: United States (limited), Various
Similar cartridges: .38 Super, 9mm Luger