.300 Winchester Magnum

Winchester introduced the .300 Winchester Magnum in 1963 as the last and largest of a family of belted magnums built by shortening and necking down the old .375 Holland & Holland Magnum case to fit a standard-length rifle action. Where the .264 and 7mm and .338 Winchester Magnums that came before it were built around lighter bullets for particular game, the .300 was aimed squarely at the biggest standard-length bolt actions could handle, and it has stayed the commercial standard for long-range hunting and military and police sniping in that case size ever since.

The belt is the tell: a narrow raised band just ahead of the extractor groove, inherited from the .375 H&H’s need to headspace off something other than a shoulder cut for a double rifle. On the .300 Winchester Magnum the belt does no real work — the shoulder alone would headspace the round fine — but the case carries it anyway, as every round in the family does. Behind a 25-degree shoulder sits a case just 66.55 mm long holding a 7.85 mm bullet to a C.I.P. maximum overall length of 84.84 mm, at up to 430 MPa (C.I.P.) or 64,000 psi (SAAMI, measured by a different method and not the same number). US and allied sniper rifles built on the Remington 700 action, including the Army’s XM2010 Enhanced Sniper Rifle, are chambered for it specifically because it fits an unmodified short/long bolt face while outranging 7.62x51mm NATO.

Two Federal factory loads are recorded here for their published ballistic coefficients: a 200-grain Terminal Ascent hunting bullet and a 180-grain Barnes TSX, both bonded or solid-copper designs built to hold together on heavy game.

Gaps on this page: neither Federal product page states a test barrel length, so no muzzle velocity is recorded for either load — Federal states barrel length on some of its pistol lines but not on these rifle pages, and this site does not interpolate or estimate one. No cartridge mass (loaded round, not bullet) is published for either load.