The Smith & Wesson 1940 Light Rifle is one of the spectacular failures of arms design, on several levels. It was too expensive, too heavy, too fragile (ironically, given the weight), too difficult to manipulate, and just all-in-all bad. To put the bad-ness in perspective, the British cancelled their order of these guns and rejected those already delivered – right in the aftermath of Dunkirk, when they were in serious need of arms. To completely reject a gun that was being actively produced and delivered under those circumstances says a lot! I had the opportunity to take a closer look at a second model M1940 S&W Light Rifle at Rock Island Auctions, and took this video:
In the Vault page on the M1940 Light Rifle, you can find a longer description of the gun’s shortcomings, as well as a copy of the manual S&W wrote for it. In addition, I have a scan of a 1969 article on them from Gun Facts magazine, in which Jan Stevenson does an excellent job of explaining the weapon’s history and eccentricities.