The Bang rifles were a series of American-Danish prototype semi-automatic rifles.
The rifle had 3 variants, the M1909, M1911 and M1922. During trials between 1919 and 1927, the rifle was demonstrated by its designer, Søren Hansen Bang, but was unsuccessful due to mechanical complexity and susceptibility to gas fouling in its action.
It was a gas-operated rifle which used a sliding muzzle cup system which was blown forward by the combustion gases while the bullet emerged from the barrel. The sliding muzzle cup pulled a piston connected to a rotating bolt, thereby unlocking it, and then pushed the bolt back upon reciprocating.