Wby Ammo .30-378 Weatherby Mag 180gr. Barnes Ttsx 20-pack. 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 3500 feet per second. Reintroduced as a Weatherby production cartridge in 1996. Specifications for Wby Ammo .30-378 Weatherby Mag 180gr. Barnes Ttsx 20-pack: Manufacturer: Weatherby Caliber: .30-378 Weatherby Magnum Number of Rounds: 20 Bullet Type: Spitzer Boat Tail (SBT) Bullet Weight: 180 grain Cartridge Case Material: Brass Muzzle Velocity: 3360 ft/s Primer Style: Centerfire Dimensions: 1.55 X 4.20 X 7.00 in Package Contents: Wby Ammo .30-378 Weatherby Mag 180gr. Barnes Ttsx 20-pack