Roy Weatherby introduced his .375 Magnum in 1945. It was based on an "improved" (that is blown-out) .375 H&H case, and uses the same .375" diameter bullets.

The Weatherby factory load for the .375 drives a 300 grain Nosler Partition bullet (BC = .398) at an advertised muzzle velocity of 2800 fps with 5224 ft. lbs. of muzzle energy. The figures downrange are as follows: 2572 fps and 4408 ft. lbs. at 100 yards; 2366 fps and 3696 ft. lbs. at 200 yards; 2140 fps and 3076 ft. lbs. at 300 yards; 1963 fps and 2541 ft. lbs. at 400 yards.

According to the 26th edition of the Hodgdon Data Manual the reloader should expect a MV of about 2700 fps from .375 Weatherby reloads when using a 270 grain bullet. Hodgdon data shows that a 270 grain bullet can be driven to a MV of 2718 fps by 78.0 grains of H4895 powder. The Hodgdon technicians used a 26" free-bored test barrel to develop this data.

According to the A-Square Handloading Manual Any Shot You Want the reloader should expect a MV of about 2700 fps from .375 Weatherby reloads when using a 300 grain bullet. A-Square data shows that their 300 grain Dead Tough bullet can be driven to a MV of 2558 fps by 88.0 grains of RL-19 powder, and 2743 fps by 92.0 grains of RL-19. The pressure of the latter load was measured at 55,100 cup. The A-Square technicians used A-Square cases and CCI 250 primers; all testing was done in a 26" test barrel.

Note: A complete article about the .375 Weatherby Magnum can be found on the Rifle Cartridge Page.