This cartridge was developed specifically for use in 1000 yard benchrest competition. It was created by simply necking the 378 Weatherby case to accept 30 caliber bullets. The standard design retains the trademark Weatherby double radius shoulder. It is a simple matter to load 250 grain Sierra Match King bullets to produce almost 3000 fps muzzle velocity without exceeding 30-06 pressure levels and that from a 26 inch barrel! Lighter bullets can be driven faster but with those this chambering offers less advantage over standard 300 Magnum chamberings. When bullets lighter than 200 grains are fired from a 26 inch barrel, this cartridge is only marginally superior to the 300 Weatherby. However, with 30 inch barrels installed, ballistic difference is significant with all bullet weights. Those looking for the ultimate long range hunting rifle for smaller species might give this rifle a hard look. A single shot rifle equipped with a 30 inch tube offers reasonable handling ease and, if chambered for this cartridge, would deliver huge doses of energy to a distant target with the flattest trajectory available. 

This text is based on information from “Cartridges of the World”, Hodgdon reloading manual, the cartridge designer and/or own resources.