If the info is here it evading my search skills.

I've got a Colt AR that was given to me as a gift (cool Father in Law).  Based on the SP24#### serial number it's a 1978 "preban" version, the lower is marked as an AR 15 A2 Sporter,  .223

Here is my question.  Just forward of the front sight the barrel is marked "CMP 5.56 NATO 1/7 HBAR.

I'm curious about the markings on the barrel, is that normal for this model or has the upper been replaced/changed? The reason I ask is that if it is stock I didn't realize that Colt was putting 1/7 barrels on that long ago.  I haven't pulled the forend but I don't see any other markings on the upper.

Thanks.

A2's came from the factory with the 1/7 Barrel. AFAIK

Does not sound right to me.  Assuming your serial no. research is correct, I would suggest the upper, or at least the barrel, is not original.  Pretty sure A2 style 1/7 barrels didn't start appearing on Colt's civilian rifles until the 80s.  HBARs didn't come into vogue until the late 80s and an HBAR-equipped rifle should have "HBAR" in the receiver rollmarks.  Does your rifle have A1 or A2 sights?  I would expect a rifle from '78 to have A1 sights.

Be advised I'm no expert, though.  This info is from memory (which ain't what it used to be).