The Winchester Super Short Magnum (WSSM) is based on a short, fat cartridge geometry with an even shorter action than existing WSM cartridge offerings. The new WSSM cartridge design offers true magnum performance in both 223 and 243 calibers - all while delivering a highly efficient propellant burn with consistent higher velocities. And by headspacing off the shoulder, the new WSSM cartridge design promotes exceptional "bench-test" accuracy. Initially offered in 223 WSSM and 243 WSSM - each of these new cartridges delivers incredible accuracy with magnum energy and velocity performance in a very short action cartridge - approximately 1/2" shorter than the existing Winchester Short Magnum! It's the flatter, faster, longer range, harder hitting varmint and thin-skinned game cartridge hunters have been dreaming about.