TRW LMR Assault Rifle Experiment Vietnam War

The TRW LMR (Low-Maintenance Rifle) was born of US experience in Vietnam, particularly the ridiculous information at first given to US troops that the M-16 required virtually no maintenance of any sort. The idea of a rifle which requires little or no maintenance is a pipe dream, but in 1971, a study was started by the Pentagon to come up with a rifle for which this was really true, and a company named TRW (Thompson-Ramo-Wooldridge) was given the contract to develop it. TRW’s LMR is a rather odd-looking assault rifle; it appears to have been built with the idea of using as little materials of any sort, and therefore has a sort of bare and spartan appearance. (In fact, the LMR actually was designed to use as few parts as possible!).

Construction was largely of lightweight, yet strong steel, finished with a new, TRW-designed coating which proved to be highly-resistant to corrosion and the elements. The LMR has perhaps the straightest, most in-line design I have ever seen in an assault rifle; unfortunately, this means that the sights had to be put on high mounts. The simple stock is adjustable for length to an extent. Operation is by gas and uses a roller-locked design powering a gas piston. The LMR had only full-automatic and safe settings, but the cyclic rate of fire is so low (450 RPM) that single shots and bursts are easy to squeeze off. (This was done on purpose; it allowed for a simpler fire mechanism.) The LMR fired from an open bolt, ejecting rounds to the left through an ejection port with a spring-loaded cover that automatically opened and closed after each case ejection. Feed was from standard M-16 magazines, which were side-mounted directly opposite of the ejection port.

Operating parts, as well as the chamber and the inside of the receiver, are coated with a dry lubricant designed by TRW to allow the LMR to function with no need for the shooter to add lubrication. The pistol grip and selector switch are an almost unmodified version of that of the M-60 machinegun. The LMR used
the standard M-16-type bayonet, but it was mounted above the muzzle, below the sight line. It could also mount the “scissors” bipod developed for the M-16. The 19.4-inch barrel had no flash suppressor or muzzle brake, nor was it intended to have one. Virtually all of the LMR prototypes were designed for the 5.56mm NATO round (the M-193 version, not the modern SS-109 rounds, which didn’t exist at the time), but at least one was designed for an experimental flechette round called the XM-216.

This round had virtually the same external dimensions as the 5.56mm M-193 NATO round (to allow it to use the same magazines). LMR development lasted until 1973. In the end, the LMR was a victim of the winding down of the Vietnam War, politics, budget cutbacks, and the “weirdness factor” of a rifle that simply looked “too futuristic.”