The 270 Winchester Short Magnum (WSM) cartridge concept proved that “magnum” doesn’t always mean bigger. It does, however, mean better. When directly compared to conventional, long-action calibers, the 270 WSM exceeds it closest comparison, the venerable 270 Winchester. Of course ballistics always are complex and depnd on bullet weight and type and the actual powder, primers and processes used.  .

Moving beyond the obvious ballistic advantages of the WSM concept, there are also huge advantages in the rifles that fire these powerhouse cartridges. Most notably, WSM rifles are built on short-action configurations.

Prior to the WSM concept, short-action cartridges capable of high muzzle velocities did so with lightweight bullets and low downrange energy. To enter the realm of high velocity and heavy knockdown energy, beefed-up, belted magnum cartridges and heavy, long action rifles were required. However, by introducing long-action, belted magnum ballistics to the world of lightweight, short-action rifles, WSM calibers have effectively rewritten the rules that govern what a hard-hitting, high velocity rifle can be. Rifles chambered in WSM calibers are simply lighter and faster handling than their long action counterparts thanks to the shorter, stiffer actions and barrels used. Recoil is also reduced thanks to the short, fat case which produces a more efficient powder burn.

Specifications

• Parent case .300 WSM
• Case type Rimless, bottleneck
• Bullet diameter .277 in (6.8 mm)
• Neck diameter .3140 in (7.98 mm)
• Shoulder diameter .5381 in (13.67 mm)
• Base diameter .5550 in (14.10 mm)
• Rim diameter .535 in (13.6 mm)
• Rim thickness .054 in (1.4 mm)
• Case length 2.100 in (53.3 mm)
• Overall length 2.860 in (72.6 mm)
• Rifling twist 1-10"
• Primer type Large rifle magnum
• Maximum pressure 65,000 psi (450 MPa)

Reference: Wikipedia and ammunition companies.