7.62mm Stoner 62 weapons in light machine gun (top) and rifle (bottom) configurations

5.56mm Stoner 63 weapons, in rifle (top) and light machine gun configurations

5.56mm Stoner 63A rifle, with detachable bipod

 5.56mm Stoner 63A rifle, with detachable bipod

5.56mm Stoner 63 carbine

diagram from original US patent, granted to Eugene Stoner for design of Stoner 62 / 63 weapon system
 

	Stoner 63A rifle (XM22)	Stoner 63A carbine (XM23)
Caliber	5.56x45mm M193
Action	gas operated, rotating bolt
Overall length	1022 mm	911 mm (679mm w. folded butt)
Barrel length	508 mm	400 mm
Weight, empty	3.72 kg	3.67 kg
Rate of fire	750 - 900 rounds per minute	740 - 800 rounds per minute
Magazine capacity	30 rounds

Eugene Stoner, one of designers of M16 rifle, left ArmaLite in about 1961 and joined the Cadillac Gage Corp. There he began development of an entirely new weapon system. It was probably the first truly modular system, that consisted of about fifteen subassemblies which could be assembled in any configuration, from an assault rifle and short carbine up to a lightweight or even a general purpose machine gun. First prototypes, chambered for 7.62x51mm NATO ammunition, appeared in 1962, known as Stoner 62. Just a year later Stoner turned out a new system, chambered for 5.56x45 M193 US service round, and known as Stoner 63. This system, developed and promoted until the early 1970s, was extensively tested by the US military as the XM22 (Stoner 63A rifle), XM23 (Stoner 63A carbine), and the XM207 (light machine gun with belt feed). The only military application of the Stoner 63 system, however, was the Mk.23 model 0 belt-fed light machine gun configuration, used in limited numbers by US Navy Special Forces and Marine Corps in Vietnam. In general the Stoner system, while having the advantages of modularity and interchangeability of parts and thus great flexibility in tactical use, is too heavy as a rifle, and too expensive and somewhat over-complicated in general. It is also somewhat dirt-sensitive and requires much attention and maintenance.
Overall, some 3,500 to 4,000 Stoner 63 weapon kits were produced between 1962 and 1971.
The Stoner 63 is more than just a single firearm; it is a modular kit, which contains about 15 sub-assemblies. Different combinations of those sub-assemblies (barrels, feed units, trigger units, sight units) allow the assembly of various firearms on the single receiver unit.
The stamped steel receiver contains an universal bolt group, with a multi-lug rotating bolt and a long stroke gas piston with gas tube. The receiver also has several sets of mounting points for attachment of all other sub-assemblies and the quick-detachable barrel. In rifle and carbine configuration, the receiver is so orientated that the gas system lies above the barrel and the feed unit mounting points are below the receiver. In all machine gun configurations, either belt or magazine fed, the receiver is turned “upside down”, with the gas system being below the barrel, and the feed unit being above the receiver. In rifle / carbine configuration the Stoner 63 system utilizes a hammer-fired trigger unit, integral with the pistol grip and triggerguard. This trigger unit allows for single shots and full auto fire, and the gun is fired from a closed bolt only. In machine gun configuration, the trigger unit has no hammer; instead, its sear interoperates with the cut in the gas piston rod, allowing only full automatic fire, and only from an open bolt. The magazine feed unit can accommodate proprietary curved box magazines for 30 rounds, and can be used both in rifle and machine gun configurations. The belt feed unit could be used only in machine gun configurations. Different rear sight units were available for various configurations, with the front sights being mounted on quick detachable barrels.

On earlier Stoner 63 system weapons, the charging handle was located on the right side of the bolt carrier; the safety and fire selector were combined in one control, located on the left side of the trigger unit. On the modified Stoner 63A system, the charging handle was attached to the gas piston rod, and projected from the top in rifle / carbine configuration, or from the bottom in MG / LMG configurations; the safety was made as separate lever at the front of the trigger guard, with the fire mode selector still located on the side of the trigger unit, above the pistol grip. The Stoner 63 system featured a variety of easily detachable fixed or folding buttstocks. The latter were available in a side-folding plastic variety, or in an under-folding stamped steel type, similar to the Kalashnikov AKS / AKMS.