As World War Two developed, the Soviet Union found that bayonets were frequently lost from its M91/30 Mosin Nagant rifles. The standard bayonet, as adopted all the way back in 1891, was a long spike attached via socket over the muzzle. Carried on the belt is was long and awkward and easily discarded, and fixed to the rifle it made an already long weapon even less mobile.
In an effort to find a solution, a selection of folding bayonets were investigated, which the best design coming form one N.S. Semin. His bayonet would ultimately be adopted as part of the M44 Carbine, but before that happened it was also tested on M91/30 long rifles. Where the M44 used a permanently attached type, the version trialed on the M91/30 used a similar socket to the original bayonet, albeit with an addition locking pin to keep it in place. Testing began in the summer of 1943, and ultimately 11,500 were made by the end of that year and another 10,000 in early 1944. They were used in active fighting, but by the spring of 1944 the M91/30 was slated to be replaced entirely by the M44 carbine and further production of the long folding bayonet ceased.
A few years ago a small batch (about 100 guns) of these rifles was located, having been refurbished and put into storage after the war. They were imported into Canada, where an anonymous collector was kind enough to give me access to film this one.