(1957) Remembering General Wyman's favorable bent toward the AR-10 design, ArmaLite had also begun work on a scaled down version of the rifle. But this design, credited to John Peck, also uses the same small barrel extension as the AR-11. After the failure of the AR-11's barrel extension in testing, work is discontinued on Peck's design. Robert Fremont and L. James Sullivan are eventually tasked with starting from scratch in scaling down the AR-10 to .222 Remington.

May: Stoner provides a brief live-fire demonstration of the prototype AR-15 for General Wyman. CONARC formally requests the purchase of 10 test rifles for the Infantry Board (five days after the 7.62mm NATO M14's official adoption is announced). After a visit to Fort Benning, Stoner begins to tweak the .222 Remington round to fit the Infantry Board's penetration requirements. First, Stoner and Sierra's Frank Snow modify the .224" 68 grain "M1 ball homologue" to 55 grains by shortening the bearing length and the boattail, while maintaining the original 7-caliber ogive and 9-degree boattail. The new projectile is also produced by Sierra. Robert Hutton uses Speer's Ballistic Calculator to estimate the muzzle velocity need to provide the desired performance at 500 yards. The results indicate a muzzle velocity of 3300fps with the 55 grain bullet will be required. Hutton begins load development with IMR 4198, IMR 3031, and an unnamed Olin ball powder. Using a Remington Model 722 with a 22" Apex bull barrel and a Lyman 25x scope, Hutton successfully perforates US helmets at 500 yards during a public demonstration. However, testing also indicates that the .222 Remington cannot achieve the required velocity without excessive chamber pressure. Stoner contacts Winchester and Remington about increasing the case capacity; Remington accepts the request. (This refusal is hardly surprising since Winchester had their own SCHV rifle and cartridge in the works.) The resulting cartridge is designated the .222 Special.