In this video I use an industrial product called Tempilaq and a simple Propane Torch to anneal Brass Cartridge cases.
Brass is generic term for an alloy of Copper and Zinc. The most common Alloy for Cartridge Cases is 70% Copper and 30% Tin. http://www.engineersedge.com/brass.htm
Brass is both malleable and ductile meaning it is easily shaped and formed and can withstand high strain loads before rupture. Brass is also a good conductor of heat and electricity as well as being a “low friction” Metal these characteristics make it an ideal material for cartridge cases. http://metals.about.com/od/properties/a/Metal-Profile-Brass.htm
As brass is worked (fired in a gun and resized etc) It work Hardens. As a result, it’s malleability decrease. Eventually leading to split necks or ruptured cases. Another potential side effect of work hardened brass can cause a negative effect on accuracy as the neck tension between annealed and hardened brass will not be the same.
The Solution is to Anneal or soften the brass. Annealing, in metallurgy and materials science, is a heat treatment that alters the physical and sometimes chemical properties of a material to increase its ductility and reduce its hardness, making it more workable. It involves heating a material to above its recrystallization temperature, maintaining a suitable temperature, and then cooling
It is important to note that the Goal is to anneal the cartridge case at the neck and shoulder and to never anneal the base or rim of the case. This area is unsupported by the chamber and should remain in a relatively hardened state to maintain it’s ductile properties. It is not necessary for this part of the case to expand and create a gas seal in the chamber and a portion of the lower case is in most cases unsupported by either the bolt face or the chamber so it must withstand the chamber pressure in excess of 60,000 PSI in rifles.
So our goal in annealing is to differentially heat treat the brass cartridge case leaving the Base of the case in a work hardened state and the neck, shoulder and mount in an annealed state.
The most important factors in heat treating are time, temperature and amount of work hardening prior to the annealing process. In general Brass anneals at 350 Celsius or about 660 degrees Fahrenheit for between 10 and 30 minutes depending on initial hardness exact alloy etc. http://che.uri.edu/course/che333/Annealing%20of%2070-30%20Brass.pdf
Because brass is a good conductor of heat we cannot hope to head the neck shoulder area in excess of ten minutes without also annealing the base. Fortunately, higher temps speed up the recrystallization process thus reducing the amount of time the heat need to be applied. This reduces the risk of softening the base and speeds up the process.
Propane Torch: http://www.amazon.com/Bernzomatic-TS8000-Intensity-Trigger-Start/dp/B0019CQL60/ref=sr_1_1?s=hi&ie=UTF8&qid=1452981366&sr=1-1&keywords=propane+Torch