Recently, I did a C7 build on my old SP guns and I am getting rid of the original lowers and the stripped uppers.  On my old SP1 with an M16A1 upper I noticed that there were absolutely NO markings on it anywhere.  ZERO.   No C or H or K.....no littel triangle proof make or square one either.  The upper is a forging and is machined EXACTLY like a Colt upper receiver right down to the typical machining marks that Colts normally have.  

 The SP1/A1 that this was stripped from was always an ultra smooth, very accurate shooter and I've always been happy with it...but it sure seems strange that the A1 upper that was put on it ( before I owned it ) wouldn't have any forge marks or proofs.  Everything else was totally G.I......

any ideas?

actually this is the A1 receiver that I stripped to build the C7....so it's a naked A1....the Colt C7 that I have is true marked and proofed....it's this old A1 that I am not sure about....I guess it's anyone's guess.

I would figure an unmarked A1 would be of really lousy workmanship but this is done very well...I can't tell it from a Colt when they are side by side except for the lack of proofs....in fact I never knew it WASN'T until uxb had me look for the forge and proof marks and I couldn't find them

Older Colt M16 uppers are marked above the ejection port, towards the barrel threads. The markings are usually faint.Some times they are so lightly stamped they are hard to see, especially if the receiver has been refinished. You should see a small triangle, & a square with a letter C in it . Maybe use a magnifying glass or different lighting to make it stand out.

Quoted: Older Colt M16 uppers are marked above the ejection port, towards the barrel threads. The markings are usually faint.Some times they are so lightly stamped they are hard to see, especially if the receiver has been refinished. You should see a small triangle, & a square with a letter C in it . Maybe use a magnifying glass or different lighting to make it stand out.

I have tried that and there may be a spot with a triangle but it is sooooo faint that I can't truly tell if it is a covered mark or if I am just seeing things