I have used Mark Lee Express Blue on two revolvers and am pleased with the results. Next time though I will use Brownell's slow rust blue. For the barrel I just drop in a section of wood pencil and plug both ends with silicone. The pieces are just going to be dunked into boiling water so it's not as though they are going into molten salts. You just need to limit the amount of air inside the barrel if you plug both ends. The barrel really does not NEED to be plugged as the bluing adds no dimension, it just seems wrong to blue the bore.