[1] During World War II, he enlisted for Aviation Ordnance in the U.S. Marine Corps and served in the South Pacific and northern China.

[1] In late 1945 Stoner began working in the machine shop for Whittaker, an aircraft equipment company, and ultimately became a Design Engineer.

In 1955, Stoner completed initial design work on the revolutionary ArmaLite AR-10, a lightweight (3.29 kg (7.25 lb)) select-fire infantry rifle in 7.62×51mm NATO caliber.

Besides featuring the Stoner bolt and carrier piston system, the AR-10 stock was in line with the bore to reduce muzzle rise, especially during automatic fire.

Because recoil does not significantly shift the point of aim, faster follow-up shots are possible, and user fatigue is reduced.

In comparison with competing rifle designs previously submitted for evaluation, the AR-10 was smaller, easier to fire in automatic, and much lighter.

[7]At the request of the U.S. military, Stoner's chief assistant, Robert Fremont along with Jim Sullivan designed the Armalite AR-15 from the basic AR-10 model, scaling it down to fire the small-caliber .223 Remington cartridge.

This was another advanced 7.62 mm rifle but used a more conventional short-stroke piston and a number of stamped parts to reduce cost.

[2] In 1990, he joined Knight's Armament Company (KAC) to create the Stoner Rifle-25 (SR-25), which currently sees military service as the United States Navy Mark 11 Mod 0 Sniper Weapon System.

They visited the Smithsonian Institution, the NRA's National Firearms Museum, and a hunting lodge owned by the gun club at Star Tannery, where they went shooting.

During this short visit, both men, intimately familiar with the other's work, shared a common bond and became friends, "not needing an interpreter to get their thoughts across.