Just looking at the guns in the film it's bound to be awesome. Will probably watch it today, and report if I can identify the LMG.Can you give more details? Like pistol grip or not, stock or spade grips, curved stick mag or straight?Also Mitrailleuse, Gardner Gun, Nordenfelt Gun.
Gardner comes the closest. There were lightweight Maxim prototypes without the water jacket, and maybe a box magazine even, but nobody bought any. The one that nominally wound up as the 08/Vickers is the one everyone stocked up on in the last days of th 1800's, and didn't get serious about it until the WWI Nineteen-teens period. I'm wondering if a director/producer/prop-man saw the Gardner's very Maxim-like lines, (Or, the Maxim it could be argued, had very Gardner like lines, down to the cocking lever looking like the Gardner's crank...) and sort of combined the two ideas for a more 1890's looking LMG concept with a bit of plausibility.
The Mitrailleuse kind of ended around 1870, and most were no better than a regular canon firing shot. Since all 50-odd barrels fired at once on many designs, and then other variants did individual cartridges or waves with levers or cranks, it barely fits the role of machinegun at all.
The Nordenfelt is a bit more likely than the Mitrailleuse, although it's Calliope gun origins and wide shape made it more of a fixed mount proposition for ships. I think most of them saw their best use as small and mid-range deck guns in the .75 and 1.00 caliber + range. More as a form of small automatic canon against torpedo boats/rammers. Not something I think anyone would bring to a ground firefight.