Experimental and production versions of the synthetic stock were fiberglass reinforced polyester plastic shell halves glued together with polyurethane foam filling in between. Experimentation with synthetic material stocks began in the late 1950s for the M14 project as at least two T44E4 rifles were fitted with black color man-made material gunstocks. James S. Lunn and others patented a reinforced fiberglass M1 Garand rifle stock in 1959. Lunn Laminates (NY) made a number of M1 reinforced fiberglass stocks. Synthetic material stocks for the M1 and M14 rifles were evaluated by the U. S. Army Infantry Board during the first half of 1960. Due to similarity with the Lunn design M1 stocks, the firm may have been involved in the 1960 development for the M14 reinforced fiberglass stock but this has not been confirmed.
General Tire & Rubber Company joined Springfield Armory in 1960 in conducting research to develop a synthetic stock for the M14 rifle. Development of this lighter, stronger stock made of fiberglass reinforced polyester plastic for the M14 proceeded in stages from 1960 until late 1965. The drawing for the final version M14 fiberglass stock is dated December 1965. Beginning in 1962, fiberglass stocks were installed on M14 rifles at the factory but it was not by Springfield Armory. The following year, Springfield Armory produced a single batch of 10,000 M14 rifles in October 1963 with synthetic material stocks.
The early synthetic material stocks had no checkering and the hole for the upper butt plate screw had a wood insert to which the wood stock upper butt plate screw was anchored. These early issue synthetic stocks were milk chocolate brown in color. At least some of these early stocks were marked on the inside of the magazine well as follows: right side top line - DM-1775-GB-2, right side bottom line - DT, left side top line - DT and left side bottom line - DM-1775-GB-1. Later-manufacture fiberglass stocks were assembled with an upper butt plate screw with a finer thread. The later upper butt plate screw is anchored to a steel nut held inside a metal bracket inside the stock. 1961 pre-production synthetic stocks were found satisfactory for mounting the M15 grenade launcher sight.
Stock ferrules on synthetic USGI stocks are either crimped or dimpled but the dimpled ferrules are not common. Military Specification MIL-S-45921A and drawing F11686427 require the ferrule to be cemented and crimped to the stock to prevent movement. Thus, it appears that dimpled ferrules are earlier production stocks.
The USGI M14 synthetic stock was designed and tested for ruggedness. Forty sample stocks were selected by the U. S. government representative during initial production and monthly thereafter. Any failure of any test of any sample stock meant the day’s production or the represented batch was rejected.<snip>....................................................
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USGI synthetic M14 stocks were made as late as 1968. The U. S. Army awarded a contract to General Tire & Rubber Company in 1968 for 500,000 synthetic M14 stocks to be used as replacement stocks. At about $2,187,000.00, the February 1968 contract was the single largest known dollar amount awarded for production of a M14 rifle part between 1965 and 2006. Reportedly, a product improvement program had been written up at the General Thomas J Rodman Laboratory at Rock Island Arsenal in the early 1970s. In 1972, the Army reorganized the arsenal system. As part of the reorganization, the Rodman Laboratory staff was reduced from 125 employees to a skeleton crew of twenty-one. The M14 stock improvement program never went any further.
