Hi Rolf,
Rust bluing usually is more durable than charcoal bluing. I use an additional trick that improves durability in any barrel finish. After bluing, browning, or heat treating, etc., and after any acid rusting solutions have been neutralized by rinsing in water, I rub a thin coat of medicated vaseline (vaseline infused with phenol) on the barrel. I then heat the barrel with a propane torch just enough to get the vaseline to smoke. I then let the barrel cool and wipe off the excess vaseline. The resulting fiinish is very tough and durable. However, it is a flat finish so the method is not appropriate if you want a glossier finish on the barrel. I've used the method on barrels for myself and friends who spend a lot of time hunting in Southeast Alaska where we get >75cm of rain annually and hunting is a steeplechase of climbing up mountains, over large downed trees, and crashing through dense brush. The finish handles the abuse very well.
With respect to casehardening, Rolf, you will get brilliant colors and a hard finish on hardware heating the steel no more than 800 degrees C (1450 Fahrenheit). If the parts are not exposed to mechanical wear (like a trigger guard), you can get by with a temperature of 730 degrees C (1375 F), which provides hardness sufficient for a rust resistant surface and nice colors. Neither of those temperatures will melt or harm silver inlays as long as they are dove-tailed in place.
dave