It’s no secret that many high ranking military and civilians in the Ordnance Department were opposed to the Small Caliber High Velocity (SCHV) program of the 1950s. They offered little encouragement and support and actually did what they could to sidetrack or completely de-rail the project.
The .222 Remington Magnum was the commercial version of a SCHV cartridge developed by Remington in cooperation with Springfield Armory. When Ordnance learned of the cartridge, the .224 Springfield, all further work was ordered to stop, the justification being that Springfield was not in the ammunition development business. It’s been said that Gene Stoner was not aware of the .224 Springfield cartridge and, had he known of it, he probably would have preferred it to the .222 Remington Special, which became the .223 Remington and the 5.56x45. Though now nearly obsolete, many today still think the .222 Rem Mag is the better of the two cartridges.
Winchester was invited to develop their version of a SCHV rifle and cartridge which they did. The rifle was the .224 Light Weight Military Rifle (LWMR). The rifle was a completely different design than the AR-10 and AR-15 prototypes, but the cartridge, the .224 Winchester was nearly identical to the Remington .222 Special. So nearly identical, in fact, that Armalite was able to chamber an updated AR-15 to feed and function with both cartridges.
Armalite had considerable pull within the Ordnance Department and Winchester saw the writing on the wall. In late 1958 they halted any further development of the LWMR. The rest is history. Below are 3 versions of the .224 Winchester cartridge, the original E1, the E2, and the uncommon steel bulleted E2.