WINCHESTER introduced the .458 Win Mag in 1956, and the .264 and .338 Magnums came along in 1958. All were based on the .300 H&H belted case, shortened to 2.5” (63.5mm) but with an overall loaded length of 3.34” (84.84mm), allowing them to function in a standard .30-06 length bolt-action. It was clear that Winchester needed a .30 calibre to fill the obvious gap in its line of cartridges.
Fred Huntington, founder of RCBS, had already necked down the .338 Win Mag to .30 calibre in 1958 and although the .30-338 gained a moderate amount of acceptance in the hunting field, most of its successes were gained in long-range target shooting.
Two years later in 1960, the Swedish munitions company AB Norma Projektilfabrik entered the market with the .308 Norma Magnum, which was ballistically identical to the .30-338, but varied enough dimensionally so as not to be interchangeable.
Gun-nuts were betting that Winchester would legitimise the .30-338, but got a big surprise when the .300 Win Mag appeared in 1963. It wasn’t a standardised version of the .30-338, but rather something entirely different. It had a case length of 2.62” (66.55mm), representing an increase of 0.12” (3.05mm) over the
