One of the first semiautomatic rifles tested by the US military was a design by a Dane named Søren Hansen Bang, which was first presented to the government in 1911. The rifles used a gas trap design which would ultimately inspire many other designers include John Garand. Basically, a sliding nosecap in front of the muzzle would capture some of the gasses from firing and be pushed forward, which in turn pulled a connecting rod and caused a lever to throw the bolt backwards. Complicated enough?
Anyway, thanks to the National Firearms Centre in Leeds, we have some photos of a .303-caliber Bang rifle sent to England for British trials. I don’t know the exact date of the trials, but the NFC lists it as a model 1927 rifle.