The first area is mostly self-explanatory. Just keep shooting at him (preferably with the revolver), and toss grenades to force him out of hiding. After he loses enough health, he will toss a smoke grenade and run away. Grab any supplies and take the M82 or keep the revolver. The second area is slightly wider. Metrac will run around on a catwalk to the right and top. Shoot the valves on the right side when he is over there. Fire will shoot out of the valve for awhile, blocking off that area from Metrac. It is best to trap him on the right or in between the two fire jets (use the object lock). Metrac will retreat again after taking too many shots and go into a third area. Resupply, then follow him. For the third area, it is best to use the M82 just because it fires more shots. and in the third area you don't have much time to be precise. Metrac is in a mounted machine gun turret, which is heavily armored. You could sit there and shoot at the turret, but you would probably run out of ammunition (although you can destroy the turret this way). Instead, shoot the generators on either side. Throw grenades at them first, then finish them off with the M82. Do the same for the other generator. The gun will power down and Metrac will get out. He will then do the same little dance he did in the other two areas: fire some shots, then launch grenades, reload, and repeat. Proceed to shoot him the same way you did before, but be careful. All the boxes except the ammo boxes and the two crates that are directly in front of you can be destroyed. When he is launching grenades, wait until the grenade is in the air, then move. This will cause the grenade to land in your previous location and not hurt you. Repeat this strategy and you should eventually win.