I’ve never seen a Colt barrel with those markings.

 

I had a A2HBAR in the 224xxx range and it did not have those markings that your photo shows.

 

That's telling us (or implying) that the barrel meets the military standards for a barrel blank, chrome molly, the bore compatibility, chrome lining and the inspections applied and passed.

As far as I can tell, it does not necessarily speak to the manufacturer and as shown, I certainly don't see the tell-tale Colt "C".

Looks rather like a contract barrel or one wishing to appear so in any case.

Since this (11595E) is supposed to apply to 'blanks' and is still present on the finished barrel - it implies that the blank was shipped at the largest finished diameter for the complete barrel. That would 'generally' mean that there is not a larger outside diameter anywhere on the barrel. Is this the case for yours. Is there no larger diameter on the barrel than that which you show as stamped?

This overall strikes me as new information so, I'm at least as curious as you are.

 

Spikes Tactical Lightweight Midlength 5.56 Rilfe Barrel, Optics Planet.

 

I cant tribute except to say thanks for posting. I have a 6600 model as well and will see if something is stamped on the bottom of my barrel as well.

 

I had a Colt model R6600 A2 HBAR rifle that I bought new in 1986 ref. S/N SP 216XXX.

The barrel was marked on top between the front sight and muzzle with the usual "C MP 5.56 NATO 1/7 HBAR", the letters M & P have no space between them.

No other makings inside the handguard area.

Sold that '86 HBAR rifle in 2002 during the ban as a pre ban rifle with a great high profit.

 

Thats how my HBAR was stamped also.

Another detail missing is the diameter of the OP's barrel under the hand guard. The photo appears to show the portion under the handguard, and a HBAR barrel should be much larger than the picture shows.

 

Like mentioned above it’s absolutely a Spikes Tactical barrel. They are good barrels. Nothing Colt about this barrel though.

 

Make mine Colt

 

I would just want to add for info that most Colt HBAR heavy contour barrels that I had have these outer barrel diameters under the handguards.

0.950" outer diameter 3/4 of the length from the rear of the handguard.

0.845" OD 1/4 of the length from the front of the handguard to the rear.