The .223 WSSM (Winchester Super Short Magnum) is a rifle cartridge produced by the Winchester Repeating Arms Company. It is a shortened .300 WSM (Winchester Short Magnum) case necked down to accept a .223 caliber bullet. It is currently the fastest .22 caliber round in the world with muzzle velocities as high as 4,250 feet per second (1,300 meters per second). A rifle is a firearm with a barrel that has a helical groove or pattern of grooves (rifling) cut into the barrel walls. ... This article does not cite its references or sources. ... The Winchester Repeating Arms Company was a prominent American maker of repeating firearms during the late 19th Century and the early 20th Century. ... . ... A guns muzzle velocity is the speed at which the projectile leaves the muzzle of the gun. ...