Here's a quick sketch I did for you guys to help understand the blue spraying technique. I would strongly suggest you practice on a scrap piece of wood or cardstock before you attempt to spray your blaster barrel.
Some tips:
Keep both the spray paint nozzle and the barrel tip moving while you paint. Sweep the spray up and down, while slowly rotating the barrel tip. This technique will help you keep an even line all the way around. you don't want one side to be way more blue than the other.
Paint SLOWLY. Several very very light coats will give you the best result. The first few coats might not even look like you've painted anything at all, but after a few more, the desired effect will begin to show itself. You don't even need to wait very long between coats, maybe 30 seconds. If you try to do it on one pass you will end up too dark, or with runs in the paint, which are no good.
The blaster barrel should never be directly in line with the paint sprayer. You will quickly cover your blaster nozzle. See my illustration. Your barrel should just kiss the edge of the paint spray cone. This technique will also help you get a slightly speckled paint effect because you're catching some of the random particles of paint along the fringe of the spray. This really works when you do coat after coat, because those speckles turn into a nice fade on the side of your barrel.
I hope that helps. Take your time!! And I didn't have purple handy when i painted mine, but if you want to use purple AND blue, put the purple down first, then the blue to a lesser degree to get that nice fade from color to color to metal.
