S&W 1940 Light Rifles: Receiver Breakage is a Problem

 Designed in 1939 by S&W engineer Edward Pomeroy, the S&W Light Rifle is an extremely well manufactured but rather poorly thought out carbine. It is a 9mm Parabellum open-bolt, semiautomatic, blowback carbine feeding from 20-round magazines. It was tested by the US military at Aberdeen Proving Grounds, and rejected for a number of reasons, including not being in the US standard .45 ACP cartridge and not being full automatic. However, the British were in dire need of small arms, and S&W decided to pursue sales to the UK rather than redesign the gun to US taste.

The UK ordered a large number, but upon putting the first guns through trials found them to be unsatisfactory. The 9x19mm loading used by the British was substantially hotter than what S&W had used in designing the weapon, and receiver endcaps were shearing off in as few as 1000 rounds under British testing. The British cancelled the order, and took delivery of S&W revolvers in lieu of a refund on their (sizable) down payment. At the end of the war, all but 5 of the 1,010 guns delivered were destroyed.

In 1974, crates of leftover Light Rifles were discovered in the basement of S&W - 137 MkI types and 80 MkII  types. These were sold as a batch to Bill Orr of GT Distributors, who then sold them on the commercial market. Orr also petitioned ATF to exempt the guns from NFA short-barreled rifle classification (the guns have 9.75” barrels), and was successful - so these transfer as ordinary rifles despite their short barrels.

The difference between the MkI and MkII is the safety and the firing pin. The MkI has a lever safety which locks the bolt in the rearward position, and a floating firing pin with a lever actuator like a Beretta M38. The MkII has a rotary sleeve safety which locks the bolt either forward or rearward (a better system), and a fixed firing pin milled into the bolt face. Note that contrary to most literature, the MkII receiver was not strengthened to alleviate the durability problems found by British testing.

VIDEO HERE  (24:40 minutes)