Ok, have been searching around a bit.
First of all I think we all agree Ramon's gun is an automatic one. There's no crank visible in the movie, we don't see Ramon cranking. There's clearly two handles on the backside which would be stupid if you had to put one hand on a crank somewhere anyway. So, automatic ...
All machine gun sites I've come accross agree on one thing. The first automatic machine gun was produced by Maxim and demonstrated in 1885. They also say it was purchased by the British Army in 1889 and first used in 1893, but then again you never know who was at the demo and learned a thing or two there

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So if Leone was true to history it gives us a minimum timing for FOD. However I've not seen a single picture resembling the Ramon gun, so I stick with Harmonica's first opinion, it's just a cool looking prop.