.300 Win Mag

.300 Winchester Magnum
.300 Winchester Magnum flanked by its parent cartridges: the .338 Winchester Magnum (left) and the .375 H&H Magnum (right).
Type	Rifle, Large game
Place of origin	United States
Production history
Designer	Winchester Repeating Arms Company
Designed	1963
Specifications
Parent case	.375 H&H Magnum
Case type	Belted, bottleneck
Bullet diameter	.308 in (7.8 mm)
Neck diameter	.339 in (8.6 mm)
Shoulder diameter	.489 in (12.4 mm)
Base diameter	.532 in (13.5 mm)
Rim diameter	.532 in (13.5 mm)
Rim thickness	.049 in (1.2 mm)
Case length	2.62 in (67 mm)
Overall length	3.34 in (85 mm)
Case capacity	93.8 gr H2O (6.08 cm3)
Rifling twist	1:10 (254 mm)
Primer type	Large rifle magnum
Maximum pressure (C.I.P.)	62,366 psi (430.00 MPa)
Maximum pressure (SAAMI)	64,000 psi (440 MPa)
Maximum CUP	54,000 CUP
Ballistic performance
Bullet mass/type Velocity Energy 165 gr (10.7 g) GMX 3,260 ft/s (990 m/s) 3,893 ft·lbf (5,278 J) 180 gr (11.7 g) BT 3,146 ft/s (959 m/s) 3,972 ft·lbf (5,385 J) 190 gr (12.3 g) BTSP 3,083 ft/s (940 m/s) 4,027 ft·lbf (5,460 J) 200 gr (13.0 g) Partition 3,029 ft/s (923 m/s) 4,092 ft·lbf (5,548 J) 220 gr (14.3 g) Sierra MatchKing (HPBT) 2,850 ft/s (870 m/s) 3,908 ft·lbf (5,299 J)
Test barrel length: 24 inches (61 cm) Source(s): Accurate Powders load guide v3.5 Hodgdon powders achieve approx 100fps less.

The .300 Winchester Magnum (also known as .300 Win Mag or 300WM) (7.62×67mm) is a belted, bottlenecked magnum rifle cartridge that was introduced by Winchester Repeating Arms Company in 1963. The .300 Winchester Magnum is a magnum cartridge designed to fit in a standard rifle actions. It is based on the .375 H&H Magnum, which has been blown out, shortened, and necked down to accept a .30 caliber (7.62 mm) bullet.

The .300 Winchester is extremely versatile and has been adopted by a wide range of users including hunters, target shooters, military units, and law enforcement departments. Hunters found the cartridge to be an effective all-around choice with bullet options ranging from the flatter shooting 165 grain to the harder hitting 200+ grain selections available from the factory. The .300 Win Mag remains the most popular .30 caliber magnum with American hunters, despite being surpassed in performance by the more powerful .300 and .30-378 Weatherby Magnums and the newer .300 Remington Ultra Magnum. It is a popular selection for hunting moose, elk, and bighorn sheep as it can deliver better long range performance with better bullet weight than most other .30 caliber cartridges. Military and law enforcement departments adopted the cartridge for long range sniping and marksmanship. As a testament to its accuracy, since its introduction it has gone on to win several 1,000-yard (910 m) competitions.

Prior to the design of the .300 Winchester Magnum there were several cartridges that provided what could be best described as a magnum level of energy. The heritage of .30 caliber (7.62 mm) magnums can be traced back to the .30 Newton in 1913 and to the .300 H&H Magnum in 1925. Beginning with the .270 Weatherby Magnum in 1943, Roy Weatherby introduced a line of cartridges based on a standard length (2.5 in [63.50 mm]) magnum case. This was accomplished by taking the .30 Super Belted Rimless H&H case and having it blown out (reducing the taper) and shortened so that it could be cycled through a standard length bolt-action rifle. Then in 1944 he designed the .300 Weatherby Magnum, which essentially was an improved version of the .30 Super Belted Rimless H&H, a close variant of the .300 H&H Magnum.