Once Eugene Stoner, designer of the AR-15/M-16 series of combat rifles, left Armalite Corporation in the early 1960s, he decided to design a unique weapons platform that used a common receiver around which a family of small arms could interchange. Such a commonality would enable it to transform into a rifle, carbine or light machine gun without using special tools, and would be inexpensive and simple enough for mass production.

To see the project through, Stoner convinced Cadillac Gage, a U.S. military contractor, to provide financial aid to establish a new small arms development branch of the company. Afterward, he enlisted the aid of his two assistants at Armalite, James Sullivan and Robert Fremont, to help sort out the fine details of the idea beginning to be traced by his drafting pencil.

Throughout the months, the three discussed and disagreed, and drew diagrams to form a new weapon system that would use the standard 7.62×51 mm round used by the M-14.  Designated the Stoner Model 69W, the three saw the first handful of prototypes come off the assembly line in 1962. After the first batch of testing started, Stoner’s busy mind suggested that the next version for production should forgo the .30 caliber round in favor of the increasingly popular 5.56x45mm .223 cartridge of his M-16 rifle. The next group incorporated the change and was designated the Stoner 63 with the first ones produced in early 1963. Like the M-16 series, the Stoner used plastics instead of wood when necessary, but unlike the M-16, it used a gas piston instead of the direct impingement method for operation.

An interested party at The Defense Advanced Research Projects Agency, or DARPA, as it is better known, quickly purchased 25 units in their various configurations for testing. Later that year, the Marine Corps Landing Force Development Center in Quantico, Virginia started their tests, which reflected positively on the design by users who complemented its light weight and ammunition capacity. Still using the M-14 as their primary rifle, the Marines focused on the Stoner 63 in its light machine gun role, and continued testing, which saw the glowing reports dissipate as problems arose.

Chief among these were requirements, some say unrealistic, for the weapon to function with a wide variety of ammunition types with extreme differences in port pressures. These differences in port pressures caused cartridges to jam often. The Stoner 63 wasn’t alone either, because the still-new M-16 was having problems as well, and could not meet the requirements.

After several more months of the trials it was decided that the Stoner 63 was too unreliable for general issue and recommendations were made for improvements. 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, which didn’t reach production until 1966. Even so, they were hurriedly deployed to South Vietnam in small numbers, and in some of the most appalling conditions imaginable, the Stoner began to forge a reputation for itself not with the average G.I. or Marine, but with the Navy SEALs who used the preferred version, the LMG, to deadly efficiency.

Using box or drum magazines, carrying 100 to 150 linked rounds respectively, the Stoner 63 rattled along at a 700 rpm cyclic rate, providing valuable fire support to the small teams plying the swamps and jungles of the Mekong Delta when engaging enemy forces at close range. Excellent at fighting through ambushes or breaking contact, the gun was an immediate hit and desirable alternative to the other U.S. weapon used for such roles, the M-60. The Stoner 63A weighed much less than the M60, which required belts of ammunition to be slung over shoulders because it did not have a magazine. The M-60 was larger than the Stoner 63A and unwieldy for the types of operations SEALs performed. More impressive was its reliability, the question mark that always dogged the Stoner 63 series. Reliability remained good due to constant maintenance by the scrupulous SEALs, who made the Stoner as much a staple of their outfits as the green greasepaint they covered their faces with.

Sadly though, for its designer, this remained the Stoner 63’s only success, because, as good as reports were for the weapon in Vietnam, Eugene Stoner could not find anyone to produce the weapon. Cadillac Gage had shelved further plans beyond producing a few thousand, and the rights to make the weapon were shopped worldwide falling on deaf ears. Eventually, NWM, a weapons company in the Netherlands, agreed to acquire all licensing rights, but the deal collapsed when they were unable to secure export customers.

One last attempt to get widespread adoption in the U.S. came in 1970, when the U.S. Army issued the different variants to its Special Forces units for trials. The results were hardly encouraging, as the Green Berets found the weapons complex and fraught with pesky reliability problems. This ended Stoner’s dream of a common weapons system and, the M63 all but disappeared, except with the SEALs, whose affinity with the LMG version continued on when they used it in the 1983 Grenada invasion, and up until the late 1980s, when the Mk23 Mod 0, as it was designated, was finally withdrawn. Much though they loved it, the SEALs knew it was bastard child that found its only home and legacy among the ‘Green Faces’ who carried it with pride against the enemies of freedom.

* Article originally published on January 30, 2014 by author Mike Perry.