Originally, Tom Dornaus & Michael Dixon went to Jeff Cooper with the basic concept of making a CZ-75 clone in .45 Auto, and solicited his imput on its ideal features. After making their initial "CSP80" prototype in .45 Auto, Cooper suggested chambering it for a longer version of the old .40 G&A wildcat.
While they couldn't find a way to contact Whit Collins, Dornaus & Dixon did have a copy of his Guns & Ammo articles on the .40 G&A. Dornaus and Dixon went to John Donnelly of Ballistek to make the first prototype ammunition from .30 Remington cases. Note that in early promotional materials, the early 10mm cartridges had slightly shorter cases than what we see today. With my uncalibrated eyeball judging against a neighboring .45 ACP case, the prototype 10mm case looks closer to 23mm than the final standard of 25mm.
Then it became a matter of finding a commercial ammunition manufacturer willing to complete its development. After US ammunition manufacturers refused to cooperate, Dornaus & Dixon finally succeeded overseas with Norma. When it came time to spec-out the 10mm cartridge for Norma, Cooper suggested a muzzle velocity of 1,100 fps, so that the projectile would be guaranteed to hit its target at a minimum of 1,000 fps out to ~100 meters. When the concept of the Bren Ten Compact came up, he then suggested that the cartridge be bumped up to 1,150 fps so that the short barreled Compact could achieve the magic 1,000 fps impact velocity. Michael Dixon then told Norma to spec the cartridge for 1,200 fps, apparently thinking that Norma's test fixture barrels would run faster than the normal production pistol barrels. Norma must have added their own cushion to that figure, as they ended up delivering an early lot of 200gr ammo that clocked at ~1,250 fps from the Bren Ten.
While they couldn't find a way to contact Whit Collins, Dornaus & Dixon did have a copy of his Guns & Ammo articles on the .40 G&A. Dornaus and Dixon went to John Donnelly of Ballistek to make the first prototype ammunition from .30 Remington cases. Note that in early promotional materials, the early 10mm cartridges had slightly shorter cases than what we see today. With my uncalibrated eyeball judging against a neighboring .45 ACP case, the prototype 10mm case looks closer to 23mm than the final standard of 25mm.
Then it became a matter of finding a commercial ammunition manufacturer willing to complete its development. After US ammunition manufacturers refused to cooperate, Dornaus & Dixon finally succeeded overseas with Norma. When it came time to spec-out the 10mm cartridge for Norma, Cooper suggested a muzzle velocity of 1,100 fps, so that the projectile would be guaranteed to hit its target at a minimum of 1,000 fps out to ~100 meters. When the concept of the Bren Ten Compact came up, he then suggested that the cartridge be bumped up to 1,150 fps so that the short barreled Compact could achieve the magic 1,000 fps impact velocity. Michael Dixon then told Norma to spec the cartridge for 1,200 fps, apparently thinking that Norma's test fixture barrels would run faster than the normal production pistol barrels. Norma must have added their own cushion to that figure, as they ended up delivering an early lot of 200gr ammo that clocked at ~1,250 fps from the Bren Ten.