9×25mm Dillon

The 9x25mm Dillon, also known as the 9x25 Dillon by Dillon Precision, is a pistol wildcat cartridge developed by employees working at Dillon Precision for use in USPSA/IPSC Open guns. The cartridge is made by necking down a 10mm Auto case to 9 mm.

History
Around 1987, Eric Harvey and Randy Shelly of Dillon Precision necked down 10mm auto brass to 9mm. Their 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 IPSC Major power factor. The short-necked and steep-shouldered cartridge holds twice the powder of a .38 Super Auto case.

Others have suggested that the idea behind the 9x25mm Dillon was to use the large internal case volume of the cartridge to create a large amount of gas which upon firing would be acted upon by the compensator. The 9 mm bullet was chosen because there were already several barrel manufacturers making 9 mm-based barrels for other 9mm calibers such as the .38 Super and 9x21mm.

During the mid-1990s, gunsmiths and USPSA/IPSC shooters were looking for ways to make the compensator on IPSC Open guns more efficient. The compensator works by redirecting the gas from the fired cartridge to counteract the felt-recoil. At that time, the most popular cartridges competitors were using for Open guns were the .38 Super and 9x21mm.

The 9x25mm Dillon was used by several notable IPSC shooters, such as Rob Leatham, Armt Myhre and Michael Voigt.

Cartridge dimensions
The 9x25mm Dillon has 1.62 ml (24.9 grains) H2O cartridge case capacity.



9x25mm Dillon maximum cartridge dimensions. All sizes in millimeters (mm).

Americans would define the shoulder angle at alpha/2 = 30 degrees. The common rifling twist rate for this cartridge is 406 mm (1 in 16 in), 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 (36,259 psi) 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 9x25mm Super Auto G pistol cartridge is probably the closest ballistic twin of the 9x25mm Dillon. These cartridges are both necked down 9 mm variants of the 10 mm Auto cartridge though they dimensionally vary.

Performance and usage
The 9x25mm Dillon was a success in that there was a noticeable reduction in felt recoil, especially compared with comparable 38 Super IPSC Open guns. When fired the gun recoiled almost straight back into the shooter's hand rather than up and back. This resulted in competitors being able to fire their second shot more accurately in less time which increased their score. Another advantage was that the larger 9x25mm case could be loaded to 175 power factor at a lower pressure level than the 38 Super which extended the life of brass.

There were, however, some drawbacks to the cartridge. First (and most important given the evolution of stage design) was that since it was based on the 10 mm case, magazine capacity in a double-column 1911 magazine (such as a Strayer-Voigt or STI) was reduced by 3 to 4 rounds compared to a similar gun chambered in 38 Super or 9x21mm. Second was that some users of the 9x25mm Dillon were experiencing parts breakage on their guns at a much higher rate than a similar 38 Super&mdash;cracks in the compensator and slide and broken scopes.

The cartridge in its most effective IPSC loadings was known for an enormous shock wave that was produced when the cartridge was fired. When firing the gun, the shooter could actually feel the impulse hit their face and travel up their arm. After a while, some people began to experience tendinitis in their wrists and other soreness in their wrists and arms. For a lot of people the trade-off from reduced felt recoil and a quicker second shot wasn't worth the potential damage that could be caused to their hearing and wrists.. Some users such as Rob Leatham developed loads with less blast and shock to mitigate this, but discovered there was little advantage over a similar load in .38 Super.

The final event that spelled doom for the 9x25mm Dillon in competition use was when USPSA reduced the power factor necessary to make Major, from 175 to 165, which greatly reduced the internal pressures experienced in 38 Super guns shooting loads at Major power factor.

Reloading
Making the 9x25mm 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: At least one manufacturer, DoubleTap, currently (July 2011) offers several 9x25 Dillon factory ammunition loads.

Conversions: Drop-in barrels are available as aftermarket parts for the Glock 20 and Glock 29 semi-automatic pistols. These pistols are originally chambered by Glock for parent cartridge of the 9x25 Dillon, the 10mm Auto.