Wow, this browning stuff is kinda harsh and doesn't yield very even results. Maybe it will even out with subsequent coats but the first step sure made a lot of splotchy rust. The instructions call for rubbing it down with a coarse cloth. I had to go to steel wool to get anywhere with it. Maybe I pushed the humidity too much.
I use the LMF and also the shower as a temp & humidity box also.
You are correct in that too much humidity is not good. Also hanging parts brought in from a cooler temp room will sweat in the high humidity & temp and ruin the brown w/ droplets and sometimes water streaks.
Also apply the soln in a very thin coating. No runs or drips. Don't overlap a section of the metal that you've already covered. Don't scrub it in,,just once over and that's it.
I've had the best result with running the shower at full hot for about 2min or so. Not much more.
Close the drain,,collect the hot water in the tub. It'll help keep the temp and humidity up.
Bring in the parts and hang them or set them in the room. They'll turn a dark blue/brown in a few minutes. They should rust in a couple of hours. Sometimes I go back and turn the hot water back on for maybe 30sec again to steam up the room. Don't over do it.
Keep the door shut.
A heavier coat isn't really needed for browning, but most allow more rusting than for rust blueing. But don't let it get carried away unless you're reaching for the slightly pitted surface look. It can come about quite quickly at those higher temps and humidity ranges.
Card down each coat to remove the loose coating. I use a wire wheel. Some use wire brushes, steel wool (make sure you de-oil it before use), canvas, burlap, ect. Each will give a slightly different look as it removes a different amount of the loose coating.
Laurel Mtn will work at lower humidity and temps. Just takes longer.
I like your rifle! Wish my first LR project had turned out as well.