The Stoner 63 System was one of those “what ifs” of small arms weapons design. The basic concept behind the system was an attempt to make use of the modular idea of interchangeability: 17 core modular “units” could be assembled to produce various types of weapons for use in different roles.
This design idea had never been tried before. The system performed reasonably well in tests and saw some combat use in Vietnam (particularly with the US Navy Seals), but for various reasons it was never adopted on a wide scale.
Eugene Stoner was a brilliant and innovative weapons designer of the 1950s and 1960s. He worked for Armalite Inc. for a time and then left to pursue an independent career of his own. After much experimentation and study he came up with his modular weapons system that, he believed, would enable infantry units to respond to changing battlefield conditions extremely quickly. He apparently believed that the various small arms roles (heavy machine gun, carbine, medium machine gun, light machine gun, assault rifle, etc.) could all be satisfied by adding or subtracting from a core grouping of modular units.
His weapons were based on the so-called “rotary lock” mechanism that had been used in some Armalite weapons (AR-10 and AR-15), but he combined this with a different type of gas operation. Stoner designed his system so that the core components (receiver, bolt, piston, return spring, and trigger mechanism) could be combined with various types of bipods, tripods, and barrels to produce different weapons.
It was not exactly a “one size fits all” concept, but rather a “one group fits all” concept. Stoner marketed his system by claiming that the modular idea would enhance combat effectiveness and at the same time save money on production costs. When it became clear that the United States was moving towards the 5.56-mm round, Stoner had his guns made with this caliber.
The Stoner System was tested intensively by the US Marine Corps and the US Navy Seals in the late 1960s. Some examples even saw combat use in South Vietnam, where it proved to be a reasonably successful design. It required regular maintenance and could be a temperamental weapon, but its lightness and durability won over the operators who used it. The SEALS who used it generally praised the weapon.
But the US military was not convinced of the benefits of modular small arms systems. Production was commenced by Cadillac Gage, and there was talk of large scale contracts here and there, but in the event it all came to nothing. In retrospect it appears that the Stoner System tried to be too many things, and to fulfill too many roles. The modular concept inherently involved making some compromises, and when all was said and done, these were evidently believed to be unacceptable.
The Stoner System story remains something of a mystery, and perhaps is best filed under the heading of “cautionary tales” in small arms design.