Folks ,

The 303 magnum round is based on the 280 Ross case or the experimental 276 military round . Jeffery introduced it in 1919 . Shortened slightly and necked up for the standard 170 grain 303 projectile . It was in production from about 1919 til 1930 or so . As you noted it was purely a target round but did generate about 3200 foot pounds at the muzzle and the rifle while now a single shot , has a full set of folding express sights . This rifle has "Special BSA Barrel with 1924 BSA Rifling" along the barrel in front of the rear sights and " 303 Magnum Ex / cordite 42 170 max" on the right side of the barrel just in front of the action . On the left side of the barrel , it states " 303 Magnum cartridge / weight under 3 pounds 4 ounces " . I suspect this was a British NRA weight class . I wrote to them got a reply but no information on the classes . The sight is a Lyman base , stem , with a BSA diopter disk .

I have the official way of making the round from slightly shortened 280 Ross brass with the grains of cordite x 1.19 = grains of Reloder 15 . The much less expensive , but home engineered is to get a set of reloading dies from CH4D in Ohio and re-shape 7 mm Remington Mag brass . The belt is the same diameter as the 303 mag base and trim the brass short to the proper length . They hold up well and extract easily . So far , while I can see all the purists screaming and gasping for breath , I have reloaded some of these creations 4 - 5 times without problems and saved a lot of cash .

Specs are . . . neck 0.345 , shoulder 0.462 , base 0.530 , rim 0.557 . case length 2.35 and overall 3.25 . There is a brief note in "Cartridges of the World" 10th edition page 369 .

Jim