I have an AR-15 in standard A2 configuration the lower is all Rock River but the upper I got at a gun show, it was labled as Rock River with Colt Barrel, I know the barrel is Colt because it says C MP 5.56 NATO 1/7, it is government profile in standard no ban configuration bayonet lug, and A2 Flash Suppressor, but I'm haveing trouble identifieing the front sights there marked with what appears to be a Diamond with a B with an underflined 5 next to it inside, has anyone seen this one before, also the front handgaurd retainer appears to be triangular is this normal?....  The barrel is undated....

pictures?

Camera is put away right now, I could try getting some pictures tomorrow....

bushy bbls can be marked like that too, so that by itself does not mean its a colt

C MP is one of the markings Colt uses

B MP is a bushmaster marking.

FSB should have a "C" or a  "F" on it.

my m16a1 and m16a2 (uppers only) FSB are marked "C"
m16a1 barrel "chrome bore"
m16a2 barrel "C MP 1/7"

6721 FSB is marked "F"
6721 barrel "C MP 1/9" might HBAR as well.
there all in the safe and I am to lazy to look going from memory here.

from what I recall 20" barrels have the triangle while the 16" has the round handguard cap

My Colt 6920 FSB is marked with a diamond and a 2 as well as the F marking on the opposite side.  My LMT FSB is marked with a diamond and a 2, but no F on the opposite side.

Havn't gotten the camera out yet but heres a quit MS Paint of what the mark on the FSB sorta looks like, it's hard to see, and I'm not 100% sure what is next to the B, but it looks most like this I think....

yup, you're right, read it too fast....