The 9x25 Dillon 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 10 mm Auto case to 9 mm.
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History
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 cartidge to counteract the felt-recoil. At that time, the most popular cartidges competitors were using for Open guns was the .38 Super and 9x21. The idea behind the 9x25mm was to use the large internal case volume of the cartidge 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 a large number of barrel manufacturers making 9 mm-based barrels (such as the .38 Super and 9x21mm) and the 9 mm is inherently accurate. The 9x25mm was used by several notable IPSC shooters, such as Rob Leatham and Michael Voigt.
Effects
The 9x25mm was a success in that there was a noticeable reduction in felt recoil. When fired the gun recoiled almost straight back into the shooter's hand rather than up and back This resulted in the competitor being able to fire their second shot more accurately in less time which increased their score. There were, however, some drawbacks to the cartidge. First 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 2-4 rounds compared to a similar gun chambered in 38 Super or 9x21. Second was that some users of the 9x25mm were experiencing parts breakage on their guns at a much higher rate than a similar 38 Super - cracks in the compensator and slide and broken scopes. But the biggest drawback to the cartidge, and the one that largely contributed to it falling out of favor was the enormous shock wave that was produced when the cartidge 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.
Reloading
Making the 9x25 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 90 grains were used too.
