Notes from the Lab: .270 Weatherby Magnum

Notes from the Lab: .270 Weatherby Magnum

The .270 Weatherby Magnum was developed by Roy Weatherby by necking down the .300 H&H Magnum case to accept .277-inch bullets , while blowing out the shoulder with a double-radius to increase powder capacity. The year was 1943, and it was his first belted magnum cartridge. He soon developed many additional cartridges and began building custom rifles and offering proprietary ammunition. By 1958 the Mark V rifle was in production, the most common rifle encountered with this cartridge. With a maximum cartridge length of 3.295 inches, it will function in a standard length action.

Beginning in 1994, many Weatherby cartridges were adopted by SAAMI, which established pressure limits and chamber dimensions, etc. As a result, several ammunition companies also offer Weatherby loads including Federal, Nosler Custom, Remington and others. Weatherby factory loads currently advertise a 130-grain Barnes TSX at 3,400 fps, a 140-grain Nosler Accubond at 3,320 fps, or a 150-grain SP(Hornady or Nosler) at 3,245 fps.

Ed Weatherby claims that the .270 Weatherby Magnum is his favorite cartridge citing its flat trajectory, modest recoil and its ability to take deer, elk and pronghorn in open country. For these same reasons, it has become one of the most popular selling cartridges in the Weatherby product line.

The .270 Weatherby Magnum thrives on slow burning powders, such as Vihtavuori N-165, Hodgdon H-4831, Alliant RL-19, RL-22 and RL-25. A large rifle magnum primer is suggested to achieve reliable ignition under all field conditions. Starting loads should not be reduced or hang-fires and erratic pressures can occur.

Current industry guidelines list the .270 Weatherby Magnum with a maximum average pressure of 62,500 psi, with none of the loads in the accompanying data exceeding that limit.

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