Macro lenses tend to allow very close focus, and coupled with a longer focal length, let you get very close to your subject.
Photographing entire rifles though is not really what Macro is all about.
Wide angle lenses help you fit everything in the frame, but don't exactly give you a natural perspective on your subject either.
I see that you used 18mm on that lens. You can get wider lenses, but it is probably better to find a spot that allows you to work comfortably around the 35-50mm focal length.
Do you know how to set a custom White Balance? You can use incandecent/tungsten as the preset or you can place a white piece of paper under the light and get a custom preset. That will eliminate the "cave fire" color cast.
You want a very cheap, fast, and rather handy portrait lens?
Canon EF 50mm f/1.8 II Standard AutoFocus LensFor $70 it is almost a must have. It can focus down to about 18 inches or so, and can be used as a macro in a pinch.
Since it's fast, it allows you to shoot far more available light than your kit lens.