The Sjorgen rifle and shotgun designs definitely fit the description of Forgotten Weapons. Developed in Sweden, the Sjogren system used a fixed barrel and recoil-operated action in both a 12 gauge shotgun and .30 caliber military-style rifle. It was claimed to have very light recoil, as a result of the energy absorbed by the action cycling, though this recoil reduction was likely no more significant than today’s autoloading firearms.
Most recoil operated firearms function by having the barrel reciprocate backwards when fired, but the Sjogren system is different. It has a locking block connected to the firing pin, which keeps the bolt assembly locked in place as long as the firing pin is in the forward (fired) position. When a shell is discharged, the recoil energy must first push the firing pin backwards against its spring. This re-cocks the firing pin and also unlocks the barrel. By this time chamber pressure has dropped to a safe level, and the remaining recoil force can push the bolt back to eject the fired case and load a fresh one.
The Sjogren .30 caliber military rifle was submitted to British Army trials, but failed to garner enough interest to see further testing or use (the sample rifle tested currently resides in the British Pattern Room collection). The shotguns saw some commercial sales, and can still be found today from time to time, but were not successful enough to stay in production very long. Not much information is available on the guns, but we do have a copy of an article describing them in some technical detail from a 1908 edition of Engineering magazine.
Sjogren shotgun in 12ga photos provided by reader David (click here to download the gallery in high resolution):