The 8mm-06 Mauser,
After World War II many GI’s brought home 98K rifles captured as war trophies. Many shooters at the time found that 8mm Mauser ammo was incredibly scarce. However, 30-06 ammunition was very abundant, so hardcore shooters came up with a solution, the 8mm-06.
The 8mm-06 is a wildcat cartridge that uses a .30-06 brass casing but is loaded with an 8mm bullet. The brass would need to be reformed in order to accept the 8mm bullet, the easiest and most common method is through the use of fire forming. My dad has made many wildcat cartridges so I’m very familiar with the process. First you take an empty brass cartridge, you create a blank out of the cartridge by loading a primer, fill with gun powder (pistol powder) as well as cream of wheat (believe it or not), and then stuff in a cloth wad. Once this is done you fire the blank cartridge through the rifle. When the cartridge is discharged the brass will expand and form in the shape of the chamber. Finally you load the bullet. There is another type of 8mm-06 called the 8mm-06 Ackley Improved, which has a special taper in the casing which improves ballistics. It requires rechambering the rifle for use.
Last year my father built an 8mm-06 Ackley Improved custom hunting rifle. When he was fire forming the brass he forgot to remove the muzzle brake he had installed. When he fired a cartridge the wad blew the muzzle brake clean off the rifle.