What do you guys use for your white backgrounds? Or do you do it with editing software?
I use a 5ft wide white role of paper you can pick up from any photography store.
But you can get an inexpensive "light box" like this one
which will make for some neat pics too. They will usually come with everything you need except lights, but they have kits with lights too. You can pick up some cheap shop lights with the brightest bulbs you can find to sit on either side of the box.
You can edit the white area in Photoshop like OM has done to remove any shadows if you don't want them. I usually leave them as it adds depth to the image, IMHO. It's a matter of personal preference.
White is a good choice for backgrounds because it reflects light. With a white background you will see all the details around the firearm if it's properly illuminated as the paper reflects the light back at the subject. If you use black, it will cause more shadows to appear in many cases (depending on your light source(s)).