The Stoner 63 is a 5.56×45mm NATO modular weapon system. Using a variety of modular components, it can be easily configured as an assault rifle, carbine, top-fed light machine gun, belt-fed squad automatic weapon, or as a vehicle-mounted weapon. 

The Stoner 63 was never adopted for widespread use by American forces during the Vietnam War but was adopted by Navy SEAL teams operating in the inland waterways. It remained a favored weapon of the SEALs even after the invasion of Grenada in 1983.


Design Features of the Stoner 63

The Stoner 63 was designed by Eugene Stoner, the designer of the AR-15/M-16 in the early 1960s after he left Armalite Corporation. Stoner’s vision was to design a weapons platform that featured a common receiver around which a family of small arms could interchange. This would enable it to transform into a rifle, carbine, or light machine gun without the need for special tools. It would also make it inexpensive and simple enough for mass production. Cadillac Gage was the primary manufacturer of the Stoner 63 during its history.

Stoner initially had designed the first prototype weapon to be chambered in 7.62×51mm NATO.

Stoner 63 light machine gun
Stoner 63 light machine gun. (U.S. Navy)

Stoner designated the first weapon as the M69W. When the weapon is turned upside down the model number reads the same; this embraced Stoner’s vision of a fully invertible receiver.

Yet, while the M69W was still being developed, Stoner decided to design the next prototype around the new 5.56x45mm cartridge and eschew the iconic .30 caliber round. The 5.56x45mm cartridge was rapidly gaining favor within military circles and was used by the M-16.

The new model also used polycarbonate plastic for both the stocks and grips instead of wood.

This new weapon was called the Stoner 63 and its first models were produced in February 1963.


The Design Evolves

On March 4, 1963, the Department of Defense’s Advanced Research Projects Agency (DARPA) purchased 25 different configurations of the Stoner 63 for testing purposes. The Marine Corps Landing Force Development Center in Quantico, VA began testing the weapon in August and September 1963. 

Initial impressions of the Marines were very positive. The Marines, focusing on the light machine gun role, approved of the Stoner 63’s light weight and high ammunition capacity. 

The Army’s testing of the Stoner 63 was affected by unrealistic ammunition requirements as the weapon was expected to perform with an extremely wide range of ammunition. This affected port pressures, leaving very little power reserve with some ammunition types. In turn, this caused the weapon to jam often. The Stoner 63 wasn’t alone in facing this issue. The new M-16 failed these tests as well. 

SEALs Vietnam Stoner 63 LMG
SEAL platoon in Vietnam using the Stoner 63 LMG. (U.S. Navy)

After several more months of testing, it was decided that the Stoner 63 was too unreliable for general use, and recommendations were made for improvements on the design. These included ejection port dust covers, modifications to the feed mechanism, a stainless steel gas cylinder, a different fire selector, and improved safety. Stoner met these changes and the new weapons produced were given the designation Stoner 63A. They entered production in 1966. 


Stoner 63 Shined in the Jungles and Waterways

The Army and Marines, with the exception of the Army Special Forces and one company of Marines (Company L, 3rd Battalion, 1st Marine Regiment, 1st Marine Division), didn’t use the Stoner 63A.

However, the Navy SEALs, who liked the light machine gun (LMG) version of the weapon, used it with deadly efficiency.

Using box or drum magazines, carrying 100 to 150 linked rounds respectively, the Stoner 63 fired at a 700 rpm cyclic rate, providing valuable fire support to the small SEAL teams that were engaging in close combat along the rivers and waterways of Vietnam. 

The Stoner 63A weighed 10.5 pounds compared to an M-60’s 23, and the Stoner ammunition could be carried in magazines rather than belts of ammunition that had to be slung over shoulders. The bulk of the M-60 also made it unwieldy in many of the dense jungles that the SEALs routinely operated in. 

The Army’s Green Berets attempted trial usage in 1970 but those tests ultimately proved unfruitful. So, with just a few thousand weapons produced, production by Cadillac Gage ceased.

The SEALs still used the weapon until after the invasion of Grenada, when the military began the use of the M-249 Squad Automatic Weapon (SAW). 


Check out R. Lee Ermey fire the weapon in the YouTube video below.