That's a bubbaguns barrel :
USGI Model 653 barrel, 14.5 inches long, chrome lined, manufactured in 1996.
.625 Dia.
Barrels are marked "C MP CHROME BORE". There is an "0" stamped just if front of the barrel extension. There is no rifling twist stamped on the barrel. There is no "F" stamped on the front site base and has A2 front site posts. The barrels are 1/12. These are new in the wrap. Price is *** shipped.
This barrel has a carbine gas system with round handguard cap, and is 14.5 inches long, chrome lined, manufactured in 1996. It is marked "C MP CHROME BORE". There is an "0" stamped just in front of the barrel extension. The FSB is not “F” marked, and has A2 front site posts. The barrel is 1/12 twist, not marked on the barrel. The profile is slim forward of the handguards, and A2 under the handguards. It is marked “1/96” by the front handguard cap. I understand this is a date as the same number is on the foil bag. The part number is SP62771 with a Cage code of 13629. As far as I can tell, this is an A2 export replacement barrel.