Based on the helpful replies here, I decided to Rust Blue my barrel and figured I'd share some photos of the process.
The humidity and temperature in my basement are low so I built my own damp box out of 5/8" plywood roughly following John Bivins plans. My heat sources are two bulbs -- the bottom one is a 150w and the middle one is 60w (both on a single dimmer). The shelf on the bottom has most of the inside cut away with some coated hardware cloth over it to allow air flow. I put an old bread pan on there filled with water (I didn't make the box big wide enough to take a pie plate which would have been better). It took some experimenting to get a good temperature in humidity and if I leave the middle light off and hang a damp towel from the second hook I have in there, I get temperature and humidity in the mid-70s. If I turn the middle bulb on, temperatures get into the high 80s but the humidity lowers as well so I haven't been using it.
This is the scalding tub I made out of PVC (cutting this stuff with hand tools is a messy process and a pain in the arse):
I'm using Laurel Mountain Forge Browning Solution which is supposedly a degreaser as well but I had some trouble with the barrel not rusting near the touch hole. I think it was probably residual cutting oil left over from cutting my off-center vent liner hole
No big deal... I cleaned it off with acetone and a little steel wool and it started to take better. I'll need to hit it with a couple more coats I think and it'll be good.
I like the color -- looks like metal that has been sitting in a fire. I've never char coal blued a rifle but I'd think it would look similar.
I was up until 1am last night because I wanted to get two coats in... 3 hours in the damp box then hit it with boiling distilled water and carding (I card with a cloth). Tonight I am going to give it one more coat and hopefully it'll smooth out the remaining streakiness near the vent liner and it'll be good to go.