Stoner 63
The Stoner 63 is a 5.56×45mm NATO modular weapon system. Using a variety of modular components, it can be configured as an assault rifle, carbine, top-fed light machine gun, belt-fed squad automatic weapon, or as a vehicle mounted weapon. Also known as the M63, XM22, XM23, XM207 or the Mk 23 MOD 0 machine gun, it was designed by Eugene Stoner in the early 1960s. Cadillac Gage was the primary manufacturer of the Stoner 63 during its history. The Stoner 63 saw very limited combat use by US military units during the Vietnam War. A few were also sold to law enforcement agencies.
History
Development
Soon after leaving ArmaLite, Eugene Stoner, one of the United States' most prolific modern military small arms designers, responsible for the design of the ArmaLite AR-15/M16 assault rifles, ArmaLite AR-10 battle rifle and Armalite AR-7 survival rifle, among others, devised a concept for a modular weapon that would be built around a common receiver and certain interchangeable components and could be transformed into a rifle, carbine or various machine gun configurations by simply fitting the appropriate parts to the basic assembly.Stoner managed to solicit the help of Howard Carson, in charge of Cadillac Gage's West Coast plant in Costa Mesa, California, in convincing the company's president, Russell Baker, of the feasibility and commercial potential of his new weapons system. Baker obliged and Cadillac Gage established a small arms development branch in Costa Mesa. Stoner then recruited his two principal aides at Armalite: Robert Fremont and James L. Sullivan.
The first working prototype was chambered in 7.62×51mm NATO and completed in 1962. It was designated the Stoner M69W. 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.
Trials
On March 4, 1963, the Department of Defense's Advanced Research Projects Agency made the first purchase of the Stoner 63, ordering 25 units in various configurations. In August and September 1963, the Stoner 63 was sent to the Marines Corps Landing Force Development Center at Quantico for evaluation, where it made a positive impression with its light weight and high ammunition capacity; the Marines favored the rifle and light machine gun configurations. Trials were performed by the Army Materiel Command at their own test facilities.Many bugs affected the outcome of the Army trials of the gun: the ammunition requirements proposed were unrealistic and the weapon was expected to perform with an extremely wide range of port pressures, leaving very little power reserve with some ammunition types. For instance, the tracer ammunition used in the Stoner 63 was of such low pressure that it even failed to function reliably in the M16.
These factors severely affected the weapon's reliability. After several months of testing, the Stoner 63 system was ultimately deemed to be unacceptable for service use. The Army submitted recommendations for improvements to the design—these included a stainless steel gas cylinder, a two-position fire selector with separate safety, ejection port dust covers and modifications to the belt feed mechanism. The upgrades resulted in the improved Stoner 63A, which began production in 1966. Only about 2,000 examples of the initial version were manufactured before the transition to the model 63A.
XM207 upgrades
From 1969 to 1971 Cadillac Gage Co initiated a program to upgrade the Stoner 63 light machine gun due to Marine Corps interest. They were given one last chance to make design improvements and have a final test by the Army Materiel Command. Several changes were made to the weapon, soon to be designated "XM207 Light Machine Gun". Misfires, high cyclic rates, jams and link separations were among the issues to be resolved.
The 63A used a stack of Belleville spring washers to absorb some of the shock and bounce when the firing pin struck the primer. By changing the configuration of the washers, a higher spring rate was achieved, and this was the solution for the bulk of the misfires.
The weapon, when cold, would fire at about 650 rounds per minute. When it was very hot, after several hundred rounds had been fired, the cyclic rate climbed as high as 1,100 rpm. The mechanical functions of the weapon just would not work properly at these high rates. There were several problems that occurred at high RPM, including link separation. A "rate regulator" similar to that used in M60 machine gun was installed in the buttstock. It was basically a shock absorber that eliminated the recoil bounce off the back plate. This allowed the main drive spring to control the forward velocity of the carrier. With the "rate regulator" installed the cyclic rate of the weapon was limited to about 800 rpm. This resolved the mechanical malfunctions that occurred above 1,000 rpm. In combination with the "rate regulator" changes were made to the belt feed system for better reliability.
Another issue was low gas pressure when firing tracer rounds, causing failures to cycle. The addition of an expandable steel sealing ring in the gas chamber kept the external gas leaks to a minimum, retaining enough gas pressure to cycle the action reliably. The next issue was the polycarbonate buttstock being unable to withstand the 5,000+ pound recoil force of firing anti-tank grenades. With the weapon's tight weight restriction, using a heavier metal buttstock was not an option. Several ribbed designs were evaluated, but none were successful. The solution was to pressure-fill the hollow buttstock with a lightweight urethane foam, imparting structural rigidity and high impact strength. This solved the problem without going over the weight limit, and made the buttstock extremely durable.
Several weapons with these improvements were produced by Cadillac Gage for testing by the Army Materiel Command. This would be the last chance for the weapon, now designated XM207. With its latest design changes, the weapon passed all tests. But soon afterwards, president Nixon announced that the United States would be withdrawing from Vietnam, eliminating the urgency to adopt a new infantry weapon. The XM207 project was cancelled.
Deployment
Even very early on in its development stage, a small number of weapons were hurriedly pressed into service with the U.S. Navy SEALs deployed to Southeast Asia. During 1967, the Stoner 63A system was field tested by Company L, 3rd Battalion, 1st Marine Regiment, 1st Marine Division. Riflemen were issued the weapon in the Rifle configuration, while officers and certain other personnel received the Carbine. The Automatic Rifle configuration was deployed on a limited basis in the squad automatic role, while Lima's weapons platoon received both the LMG and MMG configurations.In 1967, Dutch firm NWM De Kruithoorn N.V. of 's-Hertogenbosch acquired licensing rights to manufacture and sell the weapon worldwide with the exception of the United States, Canada and Mexico. NWM assembled several prototypes but the company failed to secure any export customers and the weapon was withdrawn.
The Stoner 63 was also considered for the Swiss armed forces as the W+F Stgw 71 chambered in 5.6x48mm Eiger.
In 1970, the U.S. Army designated the light machine gun configuration XM207 and issued it to select Army Special Forces units for evaluation. However, due to its complexity and high maintenance requirements, the design was rejected, and the project was dropped in 1971. That same year, Cadillac Gage ceased all production of the Stoner 63. Around 4,000 63 and 63A units were built in total. The Navy SEALs continued to use the Stoner 63 and had officially adopted the Commando version as the Mark 23 Mod 0 machine gun. By the late 1980s the Stoner 63 was completely phased out in favor of the new M249 SAW, and most of the remaining guns were destroyed.
Design details
Operating mechanism
The Stoner 63 series of weapons are piston driven, air-cooled, belt or magazine-fed and in rifle and carbine configuration, fire from a closed bolt to ensure maximum accuracy, or in machine gun mode, fire from the open bolt position to prevent cook-offs and enhance cooling. The weapon has a rotary bolt locking mechanism with 7 radially symmetrical locking lugs that engage a series of recesses in the barrel extension, and is actuated by a conventional long-stroke piston. The radial arrangement of locking lugs distributes the firing load evenly around the bolt head and barrel socket, reducing stress and increasing the longevity of these critical components. Attached to the piston extension is the bolt carrier which is equipped with a curved cam track that guides the bolt's cam pin and rotates the bolt 22.5° during the movement of the piston to either lock or unlock the bolt from behind the abutments in the barrel socket. Incorporated into the bolt carrier/piston group is an anti-bounce device, consisting of a carbide rod that rides within the piston extension's hollow interior and moves back and forth during the recoil and counter-recoil cycles, reducing bolt bounce and preventing the possibility of firing out of battery during closed bolt firing.When fired, propellant gases from the ignited cartridge following the projectile down the bore are vented through a gas port into a gas cylinder where they drive the piston and bolt carrier rearward. There is about of uninterrupted free travel calculated to permit the gas build-up in the bore to drop to a safe level before the carrier's cam slot rotates the bolt counter-clockwise to unlock. The locking lugs have no pitch therefore no primary extraction occurs during the unlocking sequence. A deeply seated spring-loaded claw extractor in the bolt head extracts the spent cartridge casing from the chamber and a spring-powered ejector fixed to the front feed mechanism trigger housing ejects the casing. The bolt carrier continues to the rear and compresses the captive recoil spring on its guide rod.
The Stoner 63 has a unique buffering system contained within the bolt carrier. In front of the carrier cap are a steel shim and a set of 27 saucer-shaped Belleville washers oriented in opposing sets of three, which absorb energy from the piston stroke by deforming into a flat plate when the bolt carrier strikes the receiver's end cap. When the plates return to their original shape they release a pulse of strain energy which propels the reciprocating parts forward in counter-recoil with a speed only slightly below that of the original recoil velocity. The plates will function without failure for between 40,000 and 50,000 rounds. This feature was designed to extend the weapon's service life.