.243 Winchester Super Short Magnum

The 243 Winchester Super Short Magnum or 243 WSSM is a rifle cartridge introduced in 2003. It uses a .300 WSM (Winchester Short Magnum) case shortened and necked down to accept a .243in/6mm diameter bullet, and is a high velocity round based on ballistics design philosophies that are intended to produce a high level of efficiency. The correct name for the cartridge, as listed by the Sporting Arms and Ammunition Manufacturers' Institute (SAAMI), is 243 WSSM, without a decimal point.

Design
The 243 WSSM is an addition to the Winchester Super Short Magnum (WSSM) family of cartridges, which also include the .223 WSSM and the .25 WSSM, and the idea behind the 243 WSSM was to develop a compact, higher velocity version of the well-established and internationally popular .243 Winchester unveiled by Winchester in 1955.

The 243 WSSM's case is unusually short and fat in profile, contrasting markedly with most other rifle cartridges, and is intended to take advantage of what ballisticians have shown is the more uniform and efficient burning of propellant powder when it is held in a short, fat stack by the cartridge case.

Performance
In their ballistics tables, Winchester list a very high muzzle velocity of 4060 ft/s with a 55 gr projectile for this cartridge. Based on Hodgdon reloading data typical velocities should range from approximately 4000 ft/s with a 58 gr bullet to approximately 3000 ft/s with a 100 gr bullet. The percentage gain in performance over the older .243 Winchester is around 10% or less, and it remains to be seen if the market will offer a commercially viable place to two 6 mm sporting cartridges that have such similar performance.

This cartridge is usually used for small game such as varminting, and used for animals as large as deer.

Advantages
Compared to other factory 6mm sporting cartridges the 243 WSSM is capable of functioning in the AR-15 platform. Other factory produced 6mm cartridges like the 243 Win. and 6mm Rem. are both too long for the AR-15 and require the AR-10 platform.

The 243 WSSM is 3/8 inch shorter than the 243 Win. giving the 243 WSSM the ability to fit in a super-short action rifle. Thus 243 WSSM rifles can be lighter, have stiffer actions and have faster actions to cycle.

The 243 WSSM gives generally a 10% increase in velocity over the 243 Win.