At my local gun shop, there's a COLT AR-15 Carbine for sale. The receiver is a pre-1994 SP serial #'s AR-15.  I'm trying to determine if the uppper is original to the lower. The upper has the bayo lug and birdcage flash hider.  The the barrel is marked:

SS 5.56mm

Any thoughts on this?
Regards,
OH58D

I have never heard of a Colt barrel marked "SS 5.56" though I could be wrong.

I thought they were all marked something like:
"CMP 1/7 5.56 NATO." I think all the AR15a2's had 1/7 twist barrels and the SP1's would be marked something like:
"CMP Chrome(bore) 1/12" or something similar.

My guess is this gun has an aftermarket barrel on it. This may or may not be a good thing.

Try looking here http://www.biggerhammer.net/ as they have a very good AR15 FAQ section.

First attempt was faulty. I wonder how that happened?

This attempt works.

www.biggerhammer.net/

SS 5.56mm

That's an Olympic Arms mark.

Ditto, that is an Oly barrel.

-elliott

Thanks for the information.  I only wish there was some reference book available with all of the codes and markings for various makers.  It would be great to have this available for identifying "parts guns".

Regards,
OH58D

Actually its pretty easy for Colts. If its a preban the barrel it will be marked either, C MP B, C MP C, C MP CHROME, C MP 1/7 NATO, C MP 1/9 NATO, you get the picture? The only difference will be post bans and very early SP-1's with the MP, or 12 marking. Those are almost impossible to find anyways.