Many shooters believe the 7mm Weatherby Magnum was introduced around 1944 but this is unlikely since, unlike the .220 Rocket, .270 Magnum, and .300 Magnum, the 7mm didn't start appearing in Weatherby advertisements in the "American Rifleman" until the early 1950's. Some shooters also believe the 7mm has always been one of Weatherby's most popular cartridges but this isn't true either. Roy's 7mm enjoyed only mild popularity among American hunters until Remington introduced its 7mm Magnum in 1962. But then, the same can be said of any other 7mm cartridge. The case capacities of the 7mm Weatherby and the 7mm Remington magnums are close to the same, but freebored chambers in the Mark V rifles allows the Weatherby cartridge to be loaded with slightly heavier powder charges. This, however does not apply to custom rifles with chamber throats of standard length. The freeboring of rifle chambers has long been a controversial subject. Some say higher velocities can be reached while others say its not worth the effort. The fact that the 7mm Weatherby Magnum cartridge produces about 100 fps more velocity than the 7mm Remington Magnum probably proves who is right and who is wrong. Actually, choosing between the two is more of a case of rifle preference than any practical difference in cartridge performance. 

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