But there are other great guides out there.
This Instructable is a fantastic guide to painting aged metal and wood grain looks onto plastic guns. Seriously, you need to read this before painting a gun.
Epbot has an excellent tutorial on making a raygun from brass candle holder parts, glass bottles, and wood.
And finally, this is an excellent, although lengthy, video on how to steampunk a plastic gun, including making rivets, painting, and adding bits.