whats the boxy bit in front of the receiver do? idk what a gun is
Just a handguard, it doesn't really serve any mechanical purpose, just covers the barrel & gas tube. I'm not sure why they went with this design as opposed to a more typical M16 handguard (as was actually the case in earlier attempts to make an M16-based LMG)
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On the Colt IAR, which is a further evolution of this concept, there's also a big chunky handguard, but there it actually goes over a heat-sink around to barrel (you can see a bit of it poking out after the end of the handguard in this picture)
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The LMG doesn't have anything like that, so yeah, I don't know why they went with that design.
Is it potentially filled with water or coolant? Or maybe it's easier to swap barrels quickly with a larger guard.
Nope - the Colt LMG has neither water cooling nor a quick-change barrel mechanism. There was an earlier prototype which featured the barrel change part, but that didn't make it to the final iteration
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I was wondering why no quick-change barrel. Looking at it, that flimsy gas tube just hanging out there seems like a potential problem.
