Ok, let's do this again.
The title says Annealing Jackets. This includes fired brass cases to be used as bullet jackets. We are not discussing annealing necks for cartridge reloading.
It is important to anneal bullet jackets for best performance. No commercial bullet maker bypasses this step, and in fact some commercial bullet jackets are annealed more than once. When dealing with fired cases as jackets, this is even more important. You have no way to know how hard or soft any case is compared to another. Annealing puts all of the cases into the same condition.
Jackets need to be soft enough to engrave properly, and deform into the rifling grooves in the bore to make an effective seal. The head of a brass case that has not been fully annealed may not fill the corners of the rifling, and can give poor results. Hard jackets also increase the stress on die parts and press components, shortening the life of both.
Annealing Copper and Copper Alloys
Much misinformation exists in the firearms world regarding annealing copper & brass. Copper and it's alloys are metals of a face centered cubic structure that work hardens easily. As copper is moved or worked, the crystals are displaced or dislocated in relationship to each other. Annealing it requires raising the temperature high enough to allow the crystals to realign.
The minimum temperature required to properly anneal copper and it's alloys is easily calculated. Face centered cubic metals begin to anneal at just over half the absolute melting point. Sounds simple enough – pure copper melts @ 1356˚ Kelvin, so half of that would be 678˚ K or 405˚ C – about 761˚ F.
That is the minimum temperature for annealing pure copper. If you were to leave copper to soak at that temperature long enough it would become fully annealed. Nobody wants to wait that long. Raising the temperature reduces the time it takes to anneal. In an industrial environment, copper annealing usually takes place between 700˚C (1292˚F) to 900˚C (1652˚F). An average (85Cu 15Zn) Brass has a melting point of slightly less than copper (1213˚K), and a proper annealing range should be 650˚C to 725˚C for a short period of time. Because brass is a zinc alloy, heating times should be short to keep the zinc in the alloy.
As a frame of reference, Aluminum melts @ 659˚C or 1218˚F. If your heat source does not melt aluminum, it is not hot enough to anneal rapidly. If your heat source does not reach 750F, it will not anneal copper at all. Most kitchen appliances are not up to the annealing task, and should not be considered for this type of work. An inexpensive propane torch & a firebrick are a much better choice for annealing cases & jackets.
A word about quenching. Copper and it's alloys do not need to be quenched after heating to anneal. Quenching can reduce the oxidization, but is not part of the annealing process. Quench, air cool – it makes no difference to the copper or brass.
Some of you guys have self cleaning electric ovens. With a peak temp of 900˚F or so, and a cycle time around an hour, that should do just fine for annealing large lots of brass. A toaster oven will not do the job.
B.