Around 1987, Randy Shelley, an employee of Dillon Precision, necked down 10mm auto brass to 9mm. His goal was to get as much slow-burning powder in the case as possible in order to drive a 9mm bullet to the velocity needed to qualify for the then IPSCMajor power factor of 175. The short-necked and steep-shouldered cartridge holds twice the powder of a.38 Super Auto case. The 9×25mm Dillon was used by several notable IPSC shooters, such as Rob Leatham and Jack Barnes. Most shooters, looking at the 9×25mm Dillon today, focus on the extreme velocities of which it is capable. A 115grain bullet at 1800 fps is impressive, but more than needed for competition. There, a 115 only needed to be going a bit over 1500 fps to make Major. What competitors in the late 1980s and early 1990s who were using the 9×25mm Dillon were doing was adjusting the powder used, to produce more pressure in the compensator, or muzzle brake. A muzzle brake works by diverting gases to reduce felt recoil. The greater the gas volume, or the pressure that gas is at, the more force the compensator or muzzle brake creates. Competitors could "feed" the compensator more gases. This turned out to be too much of a good thing. The muzzle blast created by the combination proved to be tiring over the course of a match, and the resulting recoil re-direction proved hard on elbows and shoulders. Leatham developed loads with less blast and shock to mitigate this, but discovered there was little advantage over a similar load in.38 Super. What finally put an end to the 9×25mm Dillon in competition was component wear, magazine capacity and lowering of the USPSA Major power factor from 175 to 165. Barrels and compensators in high-pressure cartridges like.38 Super at Major velocities have a much shorter service life than lower-pressure ones. For maximum-permitted length magazines as used in USPSA/IPSC competition, a.38 Super magazine holds more rounds than a 9×25mm Dillon magazine. With the lowering of the USPSA power factor, safety and effectiveness of.38 Super loads improved to a point that the 9×25mm Dillon was no longer competitive and once worn out, pistols were often retired or rebuilt in.38 Super.
Cartridge dimensions
The 9×25mm Dillon has 1.48 ml H2O cartridge case capacity. 9×25mm Dillon maximum cartridge dimensions. All sizes in millimeters. Americans would define the shoulder angle at alpha/2 = 30 degrees. The common riflingtwist rate for this cartridge is 406 mm, 6 grooves, Ø lands = 8.79 mm, Ø grooves = 9.02 mm, land width = 3.07 mm and the primer type is large pistol. According to the QuickLOAD database the 9x25mm Dillon case can handle up to 250 MPa piezo pressure. Since there are no C.I.P. or SAAMI limits and data sets for wildcat cartridges this data has to be regarded with caution. The Austrian 9×25mm Super Auto G pistol cartridge is probably the closest ballistic twin of the 9×25mm Dillon. These cartridges are both necked down 9 mm variants of the 10 mm Auto cartridge though they dimensionally vary.
Reloading
Making the 9×25mm Dillon is fairly easy. Dillon Precision makes the necessary resizing die and reliable reloading data is easily found. Most people were using 115 grain bullets, but bullets with weights as low as 80 grains were used too.
Commercial availability
Loaded cartridges: As of 2016, DoubleTap offers six 9×25mm Dillon factory ammunition loads from 80 to 180 grains. Underwood Ammo offers three 9×25mm Dillon factory ammunition loads from 90 to 125 grains. Conversions: Drop-in barrels are available as aftermarket parts for the Glock 40, Glock 20 and Glock 29semi-automatic pistols. These pistols are originally chambered by Glock for parent cartridge of the 9×25mm Dillon, the 10mm Auto.
