.300 Winchester Short Magnum

.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. The cartridge overall length is 72.64 mm, cartridge case is 53.34 mm in length and the bullet diameter is .308 in (7.62 mm), which is common to all U.S. .30 caliber cartridges. The principle at work in the short magnum cartridge is the advantage of fitting larger volumes of powder in closer proximity to the primer's flash hole, resulting in more uniform, consistent ignition. In field use, this round mirrors the performance of its older counterpart, the .300 Winchester Magnum, which is based on a modified .375 Holland & Holland belted magnum casing.

The advantage to this round is ballistics that are nearly identical to the .300 Winchester Magnum, but in a lighter rifle with a shorter action. 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 fire arm.

Use and performance
The .300 WSM is used in the Western United States for elk, mule deer, and whitetail and on the plains, where long range shooting is almost always a must. While being relatively new cartridge, the .300 WSM has already had some success in benchrest shooting, although flatter trajectory rounds such as the 7 mm WSM, .270 WSM, etc., are normally preferred.

As with all high speed large game rounds, bullet construction plays a major role in terminal ballistic performance. If the gun is accurate enough for its intended purpose, what will make or break it is what the bullet does when it strikes its intended target. High velocity—extremely high in this case—cartridges have a set of problems all their own. If a bullet intended to perform perfectly in a lower velocity cartridge of the same caliber (such as .308 Winchester, or .30-06 Springfield) is used in the .300 WSM, the result is fragmentation and a shallow cavity; i.e. essentially a massive surface crater with poor penetration. With the right bullets, the .300 WSM is a devastating round on medium to heavy North American game animals. The actual bullet diameter used in this cartridge is .308 inches. Care should be taken to avoid using improper ammunition.

Muzzle velocity

 * 10.69 g (165 gr) Full Metal Jacket(FMJ): 3,223 ft/s (982 m/s)
 * 11.66 g (180 gr) Full Metal Jacket(FMJ): 3,095 ft/s (943 m/s)