First let me say of all the propane testing I've done as well as annealing in general . The orange flame only occurs right around the brass hitting 750* or above . The MAPP gas flame has orange in it from the get go and seems to get more orange as it heats up the case . I've talked with a few people about that orange flame . Right now there are two thoughts on that and I think they both can be right . 1) The carbon and or fouling from inside the neck burning off resulting in the discolored flame . I've not retested this after buying my SS wet tumbler . If I were to have very clean cases that may not happen . 2) The flame is showing the zinc breaking down at the edges of the mouth since it melts at 782* and there's some stuff going on way above my pay grade that I could not explain . I was told what may be going on but don't remember enough to even try to repeat it . So those have been my working theories to date . I don't believe it's unburned gas setting off .