Wikipedia
The Cei-Rigotti (also known as the Cei gas rifle) is an early automatic rifle created in the final years of the 19th century by Amerigo Cei-Rigotti, an officer in the Italian Army. The rifle had selective fire capabilities (single shots or burst) and was a gas operated rifle. Available information on this gun is sparse and contradictory.
According to several publications, the prototype rifle was chambered for the 6.5×52mm Mannlicher–Carcano. The gun was supposedly presented by Cei-Rigotti to his superiors in a private demonstration in 1895. An Italian newspaper reported on this event in 1900. According to another source, a demonstration was actually held publicly in Rome on June 13, 1900, when 300 rounds were fired on full automatic before the gun got so hot it seized up. Yet another source mentions a demonstration in the same year the Brescia Arsenal.
The British also ordered and tested the gun after this event, but they found it unsuitable. The exemplar found at the UK National Firearms Centre in Leeds is chambered in 7.65x53mm Mauser, as is another exemplar found in a U.S. private collection.
The rifle fed from a fixed box magazine, loaded through stripper clips. Reportedly, prototypes with magazines up to 50 rounds capacity existed.