The Farquhar-Hill was a semiauto rifle developed in Britain prior to World War 1. It was the idea of Birmingham gunsmith Arthur Hill, and financed by Aberdeen industrialist Mowbray Farquhar. The design began as a long-recoil system, but that was replaced with a unique spring-buffered gas operated mechanism before and production began.
Basically, a gas port in the barrel taps gas off to a piston, which moved about 3 inches rearward and was then caught and held by a latch. At that point, the other end of the spring would be released to move backward, pushing on the bolt and bolt carrier, unlocking and cycling the action. This gave the rifle a very light felt recoil impulse, and also buffered the bolt from potential over-pressure cartridges.
The Farquhar-Hill was chambered for the .303 British cartridge, and in its military form fed from 19-round drum magazines. A large order for 100,000 rifles was placed by the British military, but cancelled when WW1 ended. A small number of the rifles were sold in the military pattern as well as in box magazines fed sporting patterns, but Farquhar was more interested in pursuing military contracts, and would continue to work with machine gun designs going into the 1920s.
Thanks to the Institute of Military Technology for giving me access to these two rifles!