So give me your opinions on this one, I think it is all original. The odd thing is the two tone of the upper and lower. The upper is blacker than the lower. Also it does not have the screw front latch, rather a push pin. Please give your honest opinions. What I know about the gun is that I bought it from a friend several years ago and he owned it since the late 80's or so. I recall that long ago there were some Colts that shipped with mismatched color uppers.

Upper is marked CK and has a faint  proof C in a box on the front right


ETA: Better title?

I am not sure what you are asking.  Yep it looks like an SP1 that may or may not have the original upper.  It has for sure had the front push pin replaced.

It looks too black to be original to me.

What are the barrel markings?

Barrel markings are standard C MP and the chrome bore. The upper is C K marked. When did they start using a push pin for the front? It looks like others that I have seen.

I dont think Colt ever made an SP1 with a push pin.

That is an after market push pin.  It is not captured in the lower, it totally comes out of the lower.  Someone replaced the front screw pin with that push pin.

I have a screw set for the front sitting in my parts box, what about the color difference? It is just a few shades darker than the lower.

Even if it is not original, SP1s are great rifles and I personally just cant get enough retro ARs.

dont know about the upper but that looks like a front pin from a cobray m11/9mm pistol

Naw.  It's a piece sold by DPMS for just such a purpose; getting the screw out of early Colts.

Re the color difference. SP1s and 2s were (in)famous for those kinds of color differences. You don't see it much any more, with the addition of the black overcoating  but it was pretty common back in the "old days" they'd just grab whatever was on the line.

I do agree though that particular piece is fairly extreme in the color differences.

Somethings seem inconsistent with the upper, however I'm just learning and could be way off.

According to the SP1 data base your lower was produced in 1978 and falls in with these:



Notice the uppers are "CM", not "CK". I didn't see any in the SP1 data base marked "CK".

As mentioned by the others, the pivot pin is not original SP1, but an after market. Is there any indication that the front hole on the upper has been modified to match the SP1 lower? Is there a sear relief cut in the upper?

Your forging around the ejection port door is noticeably different from this pic of a 1981 SP1 (that may be because of the three year difference).  The upper corners on the 1981 curve out, not in.  The lower left corner in your photo is straight/even below the hinge.  The 1981 is uneven below the hinge, but matches the line on the lower.



So, although the upper appears to be a Colt, it doesn't look like it was original to that lower.  Again, if I'm off on this, feel free to correct it.