Weatherby 30-378 Weatherby Magnum 195gr Hammer Custom RIfle Ammo - 20 Rounds - Initially a wildcat cartridge developed by Roy Weatherby in 1959 at the request of the United States Army. This white-hot cartridge is based on the 378 necked down to 30 caliber and packed with powder. Originally billed as the world's fastest 30 caliber cartridge, it will push a 30 caliber bullet 3,500 feet per second. Reintroduced as a Weatherby production cartridge in 1996.