400 Cor-Bon (Corbon) case is a 45 Auto+P based case necked down to 40 caliber. The primer pocket was changed from large pistol primer to small pistol/rifle primer in 12/00. Test results concluded no adverse affect from switching to small primer pocket. Cor-Bon is now recommending Win. small pistol works best and if using small rifle Remington 7 1/2 works the best. Most popular auto pistols chambered for the .45 Auto can be converted to the .400 Cor-Bon cartridge.