From what i understand is FN does have a major contract for the m4's, m240, and m249's and they had soley built a plant here in the us just to get a contract for them being our military contracts require being made in usa from what i have heard. But im not sure on who makes more of what or vice versa.
FN does NOT make M4's they make M16's (and M240's and M249's like you mentioned).
http://www.fnmfg.com/