The first working prototype was chambered in 7.62×51mm NATO and completed in 1962. It was designated the Stoner M69W (for no other reason than when turned upside down it reads the same, symbolizing Stoner's vision of a fully invertible receiver). The follow-up design, called the Stoner 62, also chambered in 7.62×51mm, was intended for mass production. However, the design team decided to focus on the 5.56×45mm small caliber high-velocity cartridge, as it appeared the new round was gaining mainstream military approval. Eugene Stoner had previously worked with the cartridge when he designed the AR-15. The weapon system using the smaller cartridge was known as the Stoner 63. The first models were produced in February 1963. The Costa Mesa facility produced 234 Stoner 63s, when production was then moved in September 1964 to the Cadillac Gage plant in Warren, Michigan. With the change in manufacturing plants, polycarbonate plastic was used for the stocks and grips instead of wood. The weapon is covered under .