Remember water cooled guns? Well, YOU probably don’t, but they work quite well and have the side benefit of being able to make tea due to the hot water it generates. Sure, it weighs about the same as a small black hole, but it was a really effective cooling system.
Now, barrels get cooled by letting them sit when they get too hot until the air around them has sufficiently cooled them off. So naturally, someone had to go and build a heatsink and a cooling fan for the AR-15.
Obviously they look very silly, but I honestly must end my nark there, since I was prepared to write something making fun of it until I remembered that the Lewis gun used a finned barrel and was designed that the muzzle blast pulled air through the cooling shroud.
Since this is now the 21st century, we have this marvelous invention called electricity in all of the places, so a small battery fan is easy.
And really, the Lewis gun did it, so I can’t really complain. It’s not like it was first done on a really poor gun design, although it still looks stupid, but not as bad as making the fan require a 110v line feed to run.