Origin: Switzerland
Year: 1931
Type: Straight-pull bolt action rifle
Caliber: 7.5x55mm
Weight: 4.0 kg (8.82 lb) empty
Length: 1,105 mm (43.50 in)
Barrel length: 652 mm (25.67 in)
Capacity: 6 rds

Though bearing a strong resemblance to the older Schmidt-Rubin rifles and carbines which it replaced, the Karabiner 31 (K31) was actually a new design developed by Adolf Furrer, a Swiss weapons designer who is perhaps more well-known for the Furrer LMG25 machine gun he designed. Adopted in 1931, the K31 served the Swiss military for nearly three decades before being replaced with the Stgw57 in 1957. Though it had been replaced as standard issue, the carbine continued to soldier on in the hands of Swiss citizens due to the structure of the Swiss military. Many of the rifles were also purchased by the soldiers who were issued them at the end of their service.

One of the notable variations during the production of the K31 was the change in material used to manufacture the rifle's stock. Starting in 1946, stocks for the K31 were made from beechwood rather than the walnut of older rifles. This also impacted the condition of surplus K31 as beech was a softer material and was more easily damaged by the crampons and hobnailed boots worn by Swiss troops during drill. The K31 is also one of the few straight-pull military rifle designs. A straight-pull action is operated by pulling the bolt straight back and pushing it straight forward as opposed to the more common turn-bolt design seen in such designs as the Mauser, Mosin Nagant, and Enfield. Other notable military straight-pulls include the Lee Navy (US), the Steyr Mannlicher M.95 (Austria), and the Ross (Canada).

Thanks to Switzerland's neutrality, the K31 never saw combat aside from the occasional capturing of a downed Allied or Axis aviator during World War II. The surplus rifles remain in great condition with only finish wear and some damage to the wood furniture, something expected of any issued military rifle. The quality of the K31's construction combined with its accuracy, quality of surplus 7.5x55mm ammunition, and its generally low price on the surplus market have resulted in the rifle being quite popular with American shooters.