JM ; That's the best info I have had on it yet bar none !. It boggles my mind that "Colt" would have bought "surplus" canadian parts. Were any 16 series rifles with an upper like mine ever submitted by canadian interests in trials for the M16A2 final product ? - maybe that's how it got in US military inventory with an M16A1 barrel ?. Go figure , the more answers the more confused it gets !.

PS - for Nick - what gave you a clue to guess C7 upper earlier on ?.