300 Winchester Short Magnum (also known as 300 WSM) is a .30 caliber rebated rim bottlenecked centerfire short magnum cartridge that was introduced in 2001 by Winchester.^[1]

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300 Winchester Short Magnum
From left to right: .300 Winchester Magnum, 300 WSM, .308 Winchester, .223 Remington
Type	Rifle
Place of origin	United States
Production history
Designer	Winchester
Designed	2001
Manufacturer	Winchester
Produced	2001–present
Specifications
Case type	Rebated-rimmed, bottleneck
Bullet diameter	.308 in (7.8 mm)
Land diameter	.300 in (7.6 mm)
Neck diameter	.344 in (8.7 mm)
Shoulder diameter	.538 in (13.7 mm)
Base diameter	.555 in (14.1 mm)
Rim diameter	.535 in (13.6 mm)
Case length	2.100 in (53.3 mm)
Overall length	2.860 in (72.6 mm)
Case capacity	80.4 gr
Rifling twist	1-10"
Primer type	Large rifle magnum
Maximum pressure (C.I.P.)	63,817 psi (440.00 MPa)
Ballistic performance
Bullet mass/type Velocity Energy 150 gr (10 g) SP 3,313 ft/s (1,010 m/s) 3,657 ft⋅lbf (4,958 J) 165 gr (11 g) HP 3,223 ft/s (982 m/s) 3,807 ft⋅lbf (5,162 J) 180 gr (12 g) HP 3,095 ft/s (943 m/s) 3,830 ft⋅lbf (5,190 J) 200 gr (13 g) SP 2,822 ft/s (860 m/s) 3,538 ft⋅lbf (4,797 J)
Test barrel length: 24" Source(s): Reloading data at Accurate Powder

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The overall cartridge length is 72.6 mm. The cartridge case length is 53.34 mm. The bullet diameter is .308 in (7.82 mm), which is common to all U.S. .30 caliber cartridges. The principle at work in the short magnum cartridge is the fitting of larger volumes of powder in closer proximity to the primer's flash hole, resulting in more-uniform ignition. .300 WSM has a case capacity of 80 grains. The .30-06 Springfield holds 69 grains; .308 Winchester holds 56 grains; 30-30 Winchester holds 45 grains. The .300 Winchester Magnum has a case capacity of 93.8 grains. While providing ballistic performance nearly identical to that of the .300 Winchester Magnum, 300 WSM does this with about 14 grains less powder. The .300 WSM also head-spaces off of the case shoulder, versus the older .300 Winchester Magnum's belted head space design.

The advantage to this round is the ballistic performance is nearly identical to the .300 Winchester Magnum^[2] in a lighter rifle with a shorter action burning 8 - 10% less gunpowder. A disadvantage of cartridge case designs with relatively large case head diameters lies in relatively high bolt thrust levels exerted on the locking mechanism of the employed firearm. Also, in small ring actions the larger chamber diameter removes more steel from the barrel tenon, making it weaker radially.

The .300 WSM is adequate for hunting all big game including (but not limited to): moose, black bear, brown bear, elk, mule deer, and white-tailed deer in forests and plains where long range, flat shots are necessary. The .300 WSM is also used in benchrest shooting.

The .300 WSM has a standard bullet diameter of .308 in (7.82 mm) and takes advantage of the numerous bullet options available in that caliber.

The 300 WSM is a Delta L problem cartridge, meaning it can present unexpected chambering and/or feeding problems. The Delta L problem article explains this problem in more detail. The .300 Remington Short Action Ultra Magnum has very similar cartridge dimensions but is not interchangeable.

• .300 Remington Short Action Ultra Magnum
• .300 Winchester Magnum
• .300 Ruger Compact Magnum
• Winchester Short Magnum
• List of firearms
• List of rifle cartridges
• Table of handgun and rifle cartridges
• List of individual weapons of the U.S. Armed Forces
• 7 mm caliber
• Delta L problem