By the standards of 1905, the 6.35x16mmSR (AKA .25 ACP) was a tiny miracle. Using a semi-rimmed case, this cartridge could fit both revolvers and semi-auto handguns.
History of the .25 ACP
Loaded from the start with smokeless powder, it duplicated the ballistic performance of .22 LR rimfire and 5.75mm Velo-Dog loads while improving on both in substantive ways.
Compared to unjacketed . 22LR, it was more reliable in semi-auto pistols and produced less muzzle flash, being optimized for two-inch barrels. Compared to the centerfire Velo-Dog case, it was more compact.
While 50-grain FMJ is rightly considered marginal for self-defense, at least the high-quality 1905 FN Vest Pocket (1908 Colt Vest Pocket in the U.S.) was reliable, reasonably accurate and carried 6+1, again improving on the Velo-Dog revolvers.
At the time, no comparably small .22 semi-auto pistols even existed. In England, Webley began production of 25s in 1906.
Tiny Pistol, Big Reputation
While larger .25 ACP pistols have been made since, like the 1910 Mauser with a 3.3-inch barrel and the Soviet Korovin with 2.7-inch barrel, the subcompact form was the reason for the very existence of the .25 ACP.
Almost all major gun makers have produced something in that caliber. With the chamber pressure barely above that of rimfire and a stronger centerfire case designed for optimal extraction, this was an easy cartridge to make reliable in small carry weapons.
Magazines for .25 ACP are more efficient than for .22 LR, usually holding one more cartridge in the same-sized box.
Due to the diminutive size and weight, the Vest Pocket Pistol and its even smaller 1927 Baby Browning successor were informally known as “Ladies’ Browning.”
Besides the defensive uses, it received some notoriety in 1918 when a woman representing a competing socialist group tried to assassinate Lenin with one, scoring three hits and achieving a reliable stop (but failing to kill the target).
Although the . 25 ACP was never seriously considered for military use, a few countries issued pistols in that caliber to officers who used the guns more as badges of rank than as weapons.
That said, numerous American soldiers carried these tiny pistols as backups, with several reporting successful during the Korean War.
Used to larger guns, Chinese and North Korean soldiers failed to inspect boot tops and small pockets, allowing captured GIs to shoot their way out of brief captivity.
Beginning of the End
Domestic manufacturing eventually filled the need, but not all American-made 25s were of high quality, leading to the perception that it was a bad choice.
Jennings, Raven and other similar low-grade cast zink designs were often so loosely made as to make them unsafe due to striker slipping off the sear. The double-action Budischowsky TP-70 improved on those designs considerably.
The benchmark Browning Baby was eventually cloned, first by Bauer, then by Precision Small Arms—the latter still in production. Taurus and Beretta both produce tip-barrel models. Seecamp continues to produce a tiny .25 as well.
However, after the mid-1990s, the .25 ACP had been relegated to a niche-within-a-niche for several reasons.
Why the .25 ACP Ultimately Failed
The first reason is the price of ammunition, which was around five times higher than that of comparable-quality rimfire ammo.
While centerfire primers are more reliable, the price makes extensive practice more costly, as well as makes the lower-priced 25s less attractive than budget 22s.
The second is the growing perception of the cartridge as not merely marginal, but as inadequate.
The size of a typical criminal has grown steadily as nutrition improves, so the bullet that was slightly effective against a skinny 120-pounder lacks penetration for stopping a thug twice that size.
There’s also a greater awareness of the anecdotal failures to stop, leading to .32 ACP and .380 ACP, becoming the preferred choices for the pocket pistol. And that leads us to the third reason: Kel-Tec pistols.
Starting with the P-32 and followed by P-3AT, Kel-Tec invented locked-breech pocket pistols. The P-32 is actually lighter than many blowback 25s, and its slightly larger size makes it easier to control.
Ruger, S&W and others have followed with their own clones and original designs, giving consumers plenty of options in the subcompact category.
Tilt-barrel locked-breech spreads recoil over a much longer period than blowback, producing softer recoil with less weight.
Why Haven’t Gun Makers Fixed the .25 ACP?
For one, the grip size of the Baby Browning and similar pistols is actually too small for most people’s hands. For another, the .25 ACP simply lacks the energy to even penetrate (much less produce deep-enough wounds) with expanding ammunition.
A notable suicide case involving a .25 ACP Velo-Dog revolver had the victim shoot herself twice in the temple before getting through the skull.
The only better-performing cartridge with a truncated cone 35-grain brass bullet was banned by ATF as “armor-piercing.”
Ultimately, the .25 ACP was, historically, a caliber of last resort. Today, the .25 ACP remains viable for deep cover or as a backup, but better choices exist for most tasks in the same weight and price range.