you know the best way to texture anything is to unwrap it on to a Checkered bitmap. From that you can see where stretches and such appear so you can edit it up.
In 3D Studio Max / Gmax there is a program called Texporter, which allows you to export your UV Map. This said I think Max now has this built-in (finally!).
In photoshop (or your prefered pixel weapon), use the photo to create the material generals (in this case metal so a similar shade, with noise and a slight motion blur, with another cloud noise overlay of a similar colour soft blended)
Once that is done you'll have a nice gun but without details, which basically comes down to a fact of overlaying different colours for different areas then adding the Shadow&Light Layers.
It is remarkable how much you can do with a self-developed texture.
I always work to a black & white base image, then add in the colours later via images or general colours. As it helps allow definition.
Once that is all done, save the model ... continue to cut'n'edit what you have until it's a high polygon mesh. Use something like Melody to creat a normal map for the weapon, it'll add some nice depth with a good shader in DBP. Throw across a cubemap/spheremap/reflection shader and your pretty much golden
Don't forget to create the moving parts though. Alot of people forget that the guns top usually recoils and such.
