Reloading for the 10mm is easy. Reloading for the 10mm is a royal pain in the @ss. It’s easy because both cases and bullets are large and easy to handle. There are plenty of projectile options in .40 caliber, so it’s easy to find components. Reloading is a royal pain because the brass is so similar to .40 S&W. Actually, it’s virtually identical except for the length. Try sorting through a pile of mixed range pickups and see how much fun it is to find the 10mm cases.
The 10mm shares bullet and case diameter with the .40 S&W. Both use a .400-inch diameter projectile. The case is also nearly identical with the exception of length. The 10mm parent case is a .30 Remington while the .40 S&W parent case is a… 10mm. No big surprise there. Both have diameters that start at .425 inches at the base and narrow to .423 inches at the case mouth. The big difference is that the 10mm case is .992 inches long while the .40 S&W empty case measures .850 inches. When loaded with a projectile, those figures translate to maximum overall cartridge lengths of 1.250 inches for 10mm and 1.135 inches for .40 S&W. It doesn’t sound like much, but when you’re trying to design a pistol grip fits all hand sizes, that extra distance required makes things tricky.