Carl Pelo was a an engineer with Sako in the 1930s, and developed a series of self-loading rifles. He used a short recoil mechanism with a pair of locking flaps on the bolt, much like the Degtyarev machine guns from the Soviet Union. Pelo attempted to market his design both to the Finnish armed forces as well as the UK and Sweden, but was unable to get any interest (in Finland, this appears to have been largely the result of trying to sidestep standard military procurement channels by appealing directly to civil government authorities).

Prior to the Winter War, the Finnish Army was short on funds and did not see the value in trying to adopt a self-loading standard infantry rifle, but this opinion changed by 1940. There was not nearly enough time to develop Pelo's rifles between the Winter War and Continuation War, but by the early 1950s the Army was willing to give the gun a real chance. It performed surprisingly well in testing, but was ultimately rejected for its cartridge. The Finnish test rifles were chambered for 7.62x54R (53R in Finnish usage), and in Swedish testing 6.5x55mm. Finland decided to adopt a rifle in 7.62x39mm instead, and this made Pelo's design moot. While testing and iterations on the design continued through the 1950s (the model in today's video is a 1954 pattern), nothing was ever put into production and surviving examples are very scarce.

Thanks to Sako for giving me access to film this one from their factory museum!