promtheus type C for 300-400mm barrel, which is probably M4
firstly, who knows what barrel they're using to determine this, a 6.08 needs more volume than a 6.03
second, always be on the high side. So if you have a 300mm barrel, you want a cylinder for a 300-360mm barrel instead of a 250-310mm barrel or whatever
third, those stock barrels are terrible lol
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