One thing that can help - after you put the mask on, after rolling it, do a coat of the base color before doing a coat of the design color. That way any leaks at the edge will already match the base color.
For cutting brass, I've had good results using a jeweler's saw. Also works pretty well on plastic, but it doesn't have quite the work area behind the blade that a coping or hack saw does.
Sup! Really good tutorial dude, but im having trouble re-assembling the thing. When I try to slip the dart sled back into place, all the parts pop out at once! And when i do finally get it in without disaster rearing its ugly head, i cant fit the other half of the shell on before it falls apart again! Please help me Umdlancer, your my only hope!
Try only threading the main spring around the plunger tube a few times, and have most of it sticking out. Then after you've got a few screws in place, screw the spring into the case. This makes it a lot easier to get back together.