It is an A2 HBAR upper with a colt barrel stamped 5/95 and C MP 5.56 NATO 1/7 HBAR.  The chamber looks chromed, but I don't know about the barrel?  The muzzle has a 3 slot compensator that looks pinned in place.  Here's a pic: Brake pic Is the barrel threaded under the brake?  The brake slots are at 9, 12, and 3 o'clock with a closed bottom.  Is this comp loud?  Can I drill (carefully) to remove the pin then unscrew it?  What do I need to use to hold the barrel while removing the brake then installing a flash suppressor?  

The upper has 0.25 inch diameter holes in both mounting lugs.  The only mark is a broken A by the rear sight.  I'm guessing this is not a colt upper.  Here's a pic: upper pic   The bolt group and charging handle shows little wear and are unmarked.  The bolt compartment in the carrier looks chromed.  Here a pic: bolt group pic  

Quoted: The barrel should be threaded under the brake.  Best bet is to dremel around the pin and you may be able to remove it as it doesn't look to have been welded over. J

+1


use a dremel till the pin is loose and pull it out.





hold the barrel with some barrel clamps in a vise and remove/install

Will the pin go straight down or are they installed at an angle?  

Silver solder + oxy/acetylene torch = easy removal.