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3 prong flash hider Triangle hand guards SP1 upper SMALL PIN. SEAR CUT. NO Brass delfector No forward Assist.
Barrel marked C close tot he front near the fh and MP just below the Front sight base.
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Nothing after the MP? Should be either another C for "chamber" or B for "bore". MP means "magnetic particle tested".
Who makes small pin A1 uppers with sear cuts NOW. with No forward assist or Brass deflector.
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Now? Nobody.
There is a triangle stamped lightly on the upper otherwise there no marks on the upper.
Off hand I have been briefly told by a "sean at Colt that this is a EARLY m-16 upper and brl.
What is your opinion or thoughts.
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Well, you never know. It could always be something someone put together out of leftover parts and sold as a loss leader (I've been guilty of this myself[:D]). Chroming of chambers (which would account for a C or a C MP C) began in August of 1967; I don't know for sure but my impression has been that they were putting birdcage flash suppressors on M16s by then.
What does the slipring look liike? If it's the A2, so-called "delta" type, then you have one made from someone's odd parts. If it's the early straight style - and dull gray, not glossy black like 1970's in-the-wrap replacement sliprings I've seen - you could well have an original.
BTW, if it has the small hole and sear cut, it AIN'T SP1, it's M16[:D].