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The time for the molecular action to take place varies with the temperature, the thickness and the amount of annealing you desire. We are working with metal that is no more than .015" thick. You can anneal brass at about 400F if you hold it at that temperature for hours. With a piece of cartridge brass we want to heat the neck and shoulder high enough and long enough to anneal it without letting the base get to 220F. If you heat brass to between 700 and 800F annealing is done in the time it takes to get to that temperature. If it goes over 800F then you have to harden the brass before you can use it. The only way to harden brass is to work it so it is best to keep the temperature below 800F. Using tempilaq 750 on the inside of the neck you can tell when it is at 750F. That is as close to a perfect anneal as you can get for cartridge brass. The color of the brass is not important, If you are using a propane torch and the flame itself starts to turn yellow or orange that piece of brass is over annealed. The change in flame color tells you that materials in the brass are being released and burning. (this assumes you are working with clean brass) Obviously if your brass is oily or dirty the flames will turn color as the contaminants burn off.
In the time it takes to get the brass from 400 to 750F it has completed the process. Different thicknesses of brass and larger diameters of brass will take longer to heat in the same flame. You need to be able to regulate the time in the flame or the heat from the flame. In my annealer I regulate the flame using tempilaq to set it. As long as I am annealing the same cartridges I can be assured that they are properly annealed. When I change to a different cartridge I use tempilaq to reset the flame.
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