brou, use caution when dealing with "FN" parts - most of the time they are NOT FN at all, but merely some generic off-brand that a dealer will *say* is FN.
Major FN parts (barrels, bolt carriers) will have the FN markings. I can't tell you the number of times I have been at gun shows where a dealer will advertise AR parts as FN, when they indeed are not.
In my book, "FN" means "I have no idea who made this."
Don't try to save yourself too much money, it'll really bite you. I would strongly recommend buy any of the major parts (barrels and receivers) from an outfit like Bushmaster. You'll never regret doing so.
CMOS