.38 ACP

The .38 ACP is John Browning’s 1900 pistol cartridge, a semi-rimmed, straight-walled round introduced with the Colt Model 1900 and carried forward through the Model 1902 and 1903 pocket pistols that followed it — the slide of the era’s Colts stamps it “Calibre 38 Rimless Smokeless” rather than the modern name. It was one of the first successful smokeless, self-loading pistol cartridges on the American market and gave those early Colt autoloaders meaningfully more energy than the double-action revolvers they were competing against.

Its main legacy is downstream of itself: in 1929 Colt took the same case, loaded it to substantially higher pressure, and sold the result as the .38 Super for exactly the pistols the .38 ACP had already been chambered in — a 1911-frame gun could be re-barrelled from one cartridge to the other with no other change. The .38 Super went on to become the far more common round, particularly in practical pistol competition, while the original lower-pressure .38 ACP faded to a specialty and collector’s cartridge, still made in small quantities for original Colt pistols that are not rated for the Super’s higher pressure.

No dedicated C.I.P. datasheet exists for .38 ACP, but its dimensions match the .38 Super’s C.I.P. datasheet exactly, since the two share an identical case and bullet and differ only in loaded pressure, so this entry’s case and bullet dimensions are recorded as estimated by that comparison rather than as independently sourced. Its published maximum pressure, unlike those shared dimensions, is genuinely its own — 26,500 psi against the .38 Super’s roughly 36,500 psi SAAMI figure — and is recorded as estimated from Wikipedia’s uncited infobox. All three of the infobox’s factory loads are cited to the book Cartridges of the World, which cannot carry a verified status without a clickable source, so only bullet mass is recorded for each and no velocity or ballistic coefficient appears here.