When “9mm” Isn’t 9mm

That dog won’t hunt! This story began when a reader’s acquaintance
tried to fit a 9x19mm into a Walther PPK/s 9x17 (.380 ACP).

Having met a new handgun owner perplexed to find 9mm cartridges wouldn’t fit in his .380 Walther PPK/s, Handgunner reader Jack Walsh sent a note suggesting a discussion about 9mm cartridges. Sorting out all the various 9mm cartridges could fill a book, but we can try to cover some of the more popular examples.

The most popular “9” by a huge margin is the 9mm Parabellum, also known as the 9mm Luger and 9×19. Parabellum comes from the Latin proverb si vis pacem, para bellum (if you seek peace, prepare for war). It dates to 1902 and was developed for the Luger pistol, hence the 9mm Luger name.

The 9×19 designation indicates bullet diameter and case length in millimeters. It’s been called the perfect semi-auto pistol cartridge and features a rimless case with a deep, strong extraction groove and a strong casehead area. The ratio of cartridge length to diameter enhances feeding reliability.

In the late 19th century, semi-auto pistol designers realized it was difficult to make rimmed revolver cartridges feed reliably. One approach was bottleneck cartridges. Another adopted by Colt on its .25, .32, and .38 ACP cartridges was a “semi rim,” slightly larger than the case diameter. The 9×19 headspaces on the case mouth engaging a ledge at the front of the chamber. Its success proved the system worked.

Colt used the case-mouth system of headspacing on its rimless .380 ACP cartridge (1908). In Europe many refer to it as the 9mm Short and more formally 9x17mm under the European standard system.

These two are the “9s” American shooters are most likely to encounter.

Left to right: .380 ACP, 9mm (9x19mm) and .38 Super.

This .380 ACP Browning 1955 made in Belgium has the barrel marked as 9mm00.

9mm Examples

9x18 Ultra (9mm Police): Developed in 1936 as a possible service cartridge for the German Luftwaffe, it’s slightly more powerful than the .380 ACP, but still suitable for blowback pistols. With war imminent, the project was shelved. Around 1972 Walther revived it for use in the West German Police PP Super until it was discontinued in 1979. SIG, Mauser and Benelli also made some blowback pistols for 9x18 Ultra.

9x18 Makarov (9mm Makarov, 9mm Mak, 9x18 PM, 9x18 Soviet): Unlike almost all other nines, which use bullets of 0.355" to 0.356" diameter, the 9mm Mak uses 0.365" bullets. It’s widely used in Soviet bloc nations as a handgun and submachine gun cartridge.

9x20 SR (9mm Browning Long): Developed in 1903 along with the FN 1903 pistol. Like the Colt series, it’s semi-rimmed, hence the SR designation. It’s less powerful than the 9x19, since it was a blowback design unlike the locked-breech Luger. Sweden adopted the FN as their military sidearm in 1907. When supply was cut during WWI Husqvarna manufactured under license. Made to high standards, they became available as surplus in the U.S. in the 1960s. Many were converted via a chamber sleeve to accept .380 ACP ammunition.

9mm Examples

9×21 (9×21 IMI, 9mm IMI, 9mm Italian): Italy and some other nations prohibited private citizens from using 9×19 ammunition, as it was a “military” cartridge. To quote the late great Jeff Cooper, “silly rules provoke transparent evasions.” The 9×21 used a longer case with bullets seated deeper, so overall length (and ballistics) were virtually the same as 9×19.

9×23 Winchester (variation, 9x23mm Comp made by Starline): Intended for practical shooting competition, the 9×23 combined the rimless design, strong case head and extraction groove of the 9×19 with the 23mm case length of the .38 Super. Designed by competition enthusiast John Ricco in collaboration with Winchester, it solved feeding problems of .38 Super in double-stack magazines. Delayed by a legal battle between Ricco and Winchester, it faded with reduced USPSA/IPSC power factors — a shame as it is a very good cartridge.

9×25 Dillon: Based on a necked-down 10mm Auto case, the 9×25 Dillon produced even more pressure than the .38 Super, and with a good compensator almost eliminated muzzle rise. It had a brief run as a competition cartridge but is seldom seen at matches anymore. I most remember the ferocious muzzle blast. Can you hear me now?

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