I've been using the Brownells kit for the last couple years now at the University where I work. I have my students do bone and color case hardening on various parts of the steam engines that they build. We do use a modified crucible that reduces the exposure of air during the quench and the temperature we shoot for is about 1450. I have found over the course of hundreds of these parts that you do get better colors when you fall below the 1400 range, but much below that you won't get any appreciable hardening. Parts will warp during the quench unless they are blocked and I think this is critical to success when dealing with any firearm parts. If anyone wants to see the process I have a video that I shot of the process last semester and can posts samples of the parts that we do. It's not difficult to get good colors, but you do have to have a safe place to do this in.
