It's very difficult for the barrel to wobble due to the design in an AK AEG. Are you sure it's the barrel assembly, or is it just the front sight that's moving side to side? If it's the front sight, just remove the cleaning rod and tighten the philip's head screw on the bottom of the sight assembly until it's tight. If it's more than that, bring it in to the Gearbox and I'll show you how to disassemble it.