This is my first time going in-depth texturing hard surfaced objects. On my previous models I sorta cheated by not making proper high/low poly models for the normal maps and polypainting the diffuse map. But this time I did all the steps (that I know of). It took a long time because I encountered a lot of problems, mostly from some mistakes in the modeling stage. I fixed them the best I could and finally I got the gun into UDK without any artifacts! The texturing itself could still use a lot of work (not even finished), but this model served it's purpose teaching me the workflow/ solving common issues so I think it's better to move on (plus I can re-texture whenever I want anyway).
If your computer can support it, here's the model in 3D (uploaded to p3d.in):
Diffuse + Spec + Normal Maps + model in Maya Viewport 2.0:
Working in UDK: