This round was developed by Remington for Springfield Armoury in 1957. Remington called this round the .22 Experimental, but it was called the Cal. 224 Infantry Rifle by Springfield Armoury as part of their Small Caliber High Velocity Weapon System. It was based on a 222 Remington case that was extended to 1.85”. This is the specimen loaded with the 55gr. Sierra SP bullet. Remington received approval from the office of the Chief of Ordinance to market this cartridge commercially to what is known today as the 222 Remington Magnum.