/ vbbsmyt  
The FiatRevelli model 1914 is an interesting Italian design that fires 6.5mm cartridges at a rate of about 450 per minute. It uses a box magazine with 10 columns of 5 cartridges. As each column is emptied, the internal mechanism indexes the magazine to present the next column. The army version has a water jacket that can be filled from an external tank. Water can be pumped in continuously, overflowing into the outlet pipe, or the jacket can be topped up when needed allowing steam to exhaust into the tank. An aircraft version uses a heavy fluted aircooled barrel, and a 100round magazine.
I am happy to discuss more details of the Revelli with my Patrons, so please consider sponsoring me through www.patreon.com.