Just back from the aerial gunnery range. Crew chiefs are talking about copper colored deposits on the M240 gas pistons. Barracks lore is that the deposits are some carbon compound formed at high temp. The deposits are a bitch to remove. I've seen the same colored deposits on the adjustable gas system of my Sig 556. Its almost a plating look the color of a shiny penny. Would welcome an explanation and reference so my door gunners will view me with the propper reverence. CW2
