UK doctrine is that the GPMG (aka FN-MAG/M-240) can be operated in either the light or sustained fire role, depending on the mount. In the light role, it runs off a bipod with a crew of IIRC 2. In the sustained fire role, it operates off a tripod and you add a crew member plus several more spare barrels.

Having said that, I've heard from someone who was firing a GPMG until the barrel literally melted. They would have changed the barrel earlier, but were under heavy fire at the time and didn't have the chance. I think this was probably in Sierra Leone, although he was a little vague about exactly where.
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