You'll now have access to the Hammer and the Spectre, the last two single hand weapons. The Hammer is a very powerful and accurate revolver, but I wouldn't suggest it as magnum ammo is very scarce, and has a low maximum amount you can carry. The Spectre I found to be the most effective handgun, although you might want to add an Extended Clip to it for that extra shot. You'll see your first powersuit soldier on this level. They're large armored soldiers that carry chainguns. Use your guns to attack the lights on its shoulders and then it when it staggers and turns red, run up and do a finishing move on it or shoot it until it dies.
(The video belongs to BonersGames)
(FYI i used http://www.xbox360achievements.org/game/dark-sector/guide/
credit belongs to wickeddark)