Based on the Wikipedia article:
...it required about 7.5 imperial pints (4.3 litres) of water in its evaporative cooling system to prevent overheating. The heat of the barrel boiled the water in the jacket surrounding it. The resulting steam was taken off by flexible tube to a condenser container - this had the dual benefits of avoiding giving away the gun's location, and also enabling re-use of the water...
The story takes place in a World War I trench warfare type of setting. I have a situation in which the condenser can is taken away, and the gunner is firing the machine gun anyway. How much continuous firing will it take until the water jacket is too hot to touch? How long until the water is at a rolling boil? Until steam is bursting from the seams and obscuring the gunner's vision?
Thank you for your assistance!