I've used "Case Color Lacquer" from CSMC with 100% satisfactory results. In my case, I used a 1/4" camel's hair artist's brush to apply it directly to the metal---no need to disassemble the gun and risk buggering up the screws, etc. It is a quite thin as it comes out of the bottle, flows on evenly and dries in minutes--I applied a 2nd coat within a 1/2 hour of the first coat. The product enhances existing case colors by inhibiting a slight amber hue and may be thinned or removed with lacquer thinner.
http://www.csmcspecials.com/Case_Col...er_p/f0050.htm