It is a beltless, rebated rim cartridge, capable of handling all large North American game, as well as long-range shooting.

In the early 1980s Aubrey White and Noburo Uno of North American Shooting Systems (NASS) based in British Columbia Canada began experimenting with the full length .404 Jeffery by reducing the taper and necking it down to various calibers such as 7 mm, .308, 311, 338, 9.3 mm and .375.

Cartridges were fire formed from .404 Jeffery cases [citation needed] with the rim turned down, taper reduced and featured sharp shoulders.

Both Remington and Dakota Arms purchased the brass designed by Noburo Uno for use in their own experimentation and cartridge development.

Dakota too released their own version of the cartridge but chose not to turn down the rim and shortened the case to work in a standard length action.

SAAMI recommends that the barrel have a 6 groove contour with a twist rate of one revolution in 10 in (250 mm).

Factory loaded .30-378 Weatherby Magnum ammunition has a 150–200 ft/s (46–61 m/s) velocity advantage over the .300 RUM cartridge with any given bullet weight.

If chambered to allow bullets to seat to the lands of the rifling the large Weatherby cartridges would exhibit overpressure signs immediately.