Today, I wan to talk about the 32 ACP, one of the most widely used cartridges of its time, that today is all but dismissed. So, let's go all the way to the beginning to where this undisputed king of mouse guns began and see how the single longest continuously produced automatic cartridge has fallen into near obscurity. And remember: if you think I'm wrong, fight me in the comments; if you can prove I'm wrong, shoot me an email, I'd love to hear from you.

This story begins at the dawn of the cartridge era and follows a similar progression to previously covered cartridges. Unlike the 38 and 45, however, development of the 32 is not quite so linear or well documented, as it was never standardized for military use prior to 1900. For a more detailed explanation of bore size nomenclature, please refer to the first 3 minutes of our video on the 45 ACP. That said, we begin with the .31 caliber cap and ball revolver, a very popular option for pocket sized pistols of the time. With early revolvers, the caliber was named after the smallest inner bore diameter, before cut with rifling grooves. With 31 caliber firearms the inner bore was around .312 , and they fired lead ball anywhere from .315-.325  in diameter, depending on the manufacturer, with grooves often being slightly larger than the bullet to mitigate the effects of black powder fouling. By the mid 1800s two popular revolvers were offered in this caliber, the Colt Paterson, and Ethan Allen Pepperbox. 

From the late 1830s to the early 1850s Colt's patents allowed them to dominate the revolver market. However, Colt's successful cap and ball revolvers, had something of a downside in that they allowed Colt to become complacent when it came to the emerging advancements in metallic cartridges. In 1855, Smith & Wesson capitalized on this and acquired a patent giving them almost complete control over revolvers manufactured to use breach-loading cartridges. At the same time that metallic cartridges were becoming popular manufacturers in the US began naming them after the larger bore diameter made by the rifling grooves, one of the earliest being the S&W 32 rimfire, with a bullet and case diameter around .315 .  By the time Smith & Wesson's patent expired and other manufactures began making cartridge revolvers, the 32 S&W rimfire dominated the market, and most manufacturers, including Colt's, found it more feasible to chamber their pistols for the readily available Smith & Wesson cartridge, generically referred to as 32 rimfire.

By the late 1860s centerfire cartridges offered greater reliability and manufactures began releasing proprietary 32 caliber cartridges in wide range of dimensions to ensure that customers using their pistols also used their ammunition. One of the most widely available was the 320 Webley, released by that firm in both European and American markets. Colt adopted the cartridge and marketed it as 32 Short Colt in North America. It was into this diverse market that Smith & Wesson released their own 32 centerfire cartridge in 1878. The new cartridge maintained the .same .313-315  diameter of the rimfire, but increased the case diameter to .335  and case length to approximately .6 , allowing use of a more advanced inside-lubricated bullet. While the 32 Colt continued to use heeled, outside lubricated bullets into the 1890s, the 32 S&W gained a reputation for unmatched accuracy in the small pocket revolvers which chambered it. 

It was at this time, during 1894 and 1895, that John Browning began designing automatic pistols. His first four, large frame, designs fired the 38 S&W cartridge, which during development would first be modified to be rimless, and later produced the semi-rimmed 38 ACP. License to limited manufacture within North America of the first four designs was purchased by Colt. In 1896, Browning began redesigning the large frame blowback model into a pocket-sized, striker-fired automatic pistol, firing modified 32 Smith &Wesson cartridges, which he sent to Winchester's ammunition department for production samples to be made. While Colt delayed production and showed interest in only one of Browning's pistols, former Colt's employee and family friend Hart O. Berg, now an agent of FN in Belgium, encouraged Browning to submit his designs to FN. 

The FN company had grown out of early contracts to produce Mauser rifles and by the mid 1890s had build one of the most advanced manufacturing facilities in Belgium. After lawsuits with the German firms controlling the Mauser patent however, rifle production was halted and DWM had gained a controlling interest in the company. With a state-of-the-art factory and nothing to build, FN quickly began acquiring rights to produce bicycles and automobiles, in addition to seeking out other firearm designs.

In the Spring of 1897 John Browning took his pistol prototypes and traveled to the FN factory in Belgium. During his brief three week stay he also traveled to DWM in Germany, to get consent for pistol production. All of Browning's large frame designs were rejected, likely to avoid competition with DWM's C93 and C96 pistols already in production. The Belgians, however, were also keen on the pocket pistol concept and no objection was raised from DWM. Browning returned to Ogden with a provisional contract and created a final prototype pistol. Only three months later, in the summer of 1897 John and Matt Browning met Berg in Connecticut, where he was acquiring patents for a bicycle, and formalized their contracts. Berg traveled back to Belgium with the pistol prototype and 500 of the Winchester cartridge samples, where it is said that the pistol and all 500 rounds worked flawlessly.

The Winchester cartridges used the same .6  overall length, or 15.4mm, and .339  case diameter as the 32 S&W, with a reduced rim diameter of .356  and the addition of an extractor groove. Cartridge development done in Belgium would result in a longer case of 17mm, or .669  and a slightly smaller rim diameter of .353 . 

The FN cartridge and pistol were released for sale in Europe in 1899, and found immediate interest from the military, the pistol design was improved and the Model 1900 became an overnight success. While the US civilian and police market was dividedly embracing the 32 S&W Long and 38 S&W Special, the European market unequivocally adopted the 7.65mm Browning cartridge for personal and martial defense. In addition to production by FN and other European manufacturers, during 1899 UMC and Winchester began producing the cartridge for export. Initial cartridges from UMC used 2.5gr Walsrode Gray Shotgun powder and a 71gr bullet.

Upon seeing the enormous success of Browning's pistol and cartridge in Europe, in 1901 Colt requested upon Browning for a similarly sized pocket pistol. By 1903 the Colt Pocket Hammerless was released and the 7.65mm Browning cartridge became known as 32 ACP within the US. Initially minor variations existed between the North American and European cartridge, most notably the 32 was slightly lower in pressure and velocity. This caused issues with European pistols failing to cycle reliably. By 1902 UMC and Winchester had standardized their cartridges to work in both the FN and Colt pistols. In 1905 powder was changed to use 2.3gr Bullseye powder, and in 1912 bullet size was officially standardized at .311-.312  diameter, with earlier pistols and ammunition ranging anywhere from .308-.314 .  Typical velocity for a 71gr bullet appears to have been just over 900fps with a 3.5-4  barrel, which rivaled or surpassed many 32 revolver cartridges like the 32 S&W Long and Colt New Police.

Within the US the 32 ACP saw the height of its popularity during the 1920s in only a handful of pistols, most notably with the Colt 1903 being adopted as a general sidearm for Military Officers. However, in Continental Europe, Russia, Turkey, and China the 7.65mm Browning was widely used among Military Officers and Police personnel, as well as in civilian use, into the 1970s, with nearly every firearms manufacturer producing at least one pistol which chambered the round.

Since 1908 the 32's main rival has been the .380 ACP, know outside the US as 9mm Browning Short. Pistols of identical size and construction can typically be chambered in either caliber, however, the 32's soft shooting and accuracy made it the more popular option throughout production. Between 1900 and the 1950s, the 32 Auto was easily the most universally used pistol cartridge, rivaling the current use of 9mm since 2000.  As metallurgy and manufacturing advanced during the 1950s and 60s, pocket-sized pistols that had been dominated by the 32 began chambering more powerful cartridges like the 9mm Makarov and Luger. By the 1990s, the explosion of compact 9mm handguns had relegated the 32 ACP to use in micro pistols which were comparable in size to the classic .22 and .25 caliber vest pocket pistols. 

While compact pistols have never been known for decent sights, micro pistols are notoriously worse, combined with a 200fps loss of velocity out of the 2-3  barrels of the micro pistols, which were just tolerably comfortable to shoot with .25 ACP, and 32 auto quickly went from a respected and capable cartridge to a novelty of questionable ballistics, worthy of derision. Despite its extreme decline, the millions of pistols made for the cartridge ensured that it would continue in production.

A revival of interest during the mid 2010s, combined with advancements in bullet technology, have breathed new life into pistols that can handle the increased bullet weight and velocities, like the Colt 1903 and Walther PP, giving dedicated users ballistics that now rival the 380. The cartridge's suitability for this purpose, however, will continue to be hotly debated.