Page "Handloading" Paragraph 85

Annealing brass to make it softer and less brittle is fairly easy, but annealing cartridge cases is a more complex matter.

Since the base of the case must be hard, it cannot be annealed.

What is needed is a form of heat treatment called differential hardening, where heat is carefully applied to part of the case until the desired softness is reached, and then the heat treatment process is halted by rapidly cooling the case.

Since annealing brass requires heating it to about 660 F ( 350 C ), the heating must be done in such a way as to heat the neck to that temperature, while preventing the base of the case from being heated and losing its hardness.

The traditional way is to stand the cases in a shallow pan full of water, then heat the necks of the cases with a torch, but this method makes it difficult to get an even heating of the entire case neck.

A temperature sensitive crayon can be used at the point to which it is to be annealed, which is just behind the shoulder for bottlenecked cartridges, or at the bottom of the bullet seating depth for straight wall cartridges.

The neck of the case is placed in a propane torch flame and heated it until the crayon mark changes color, indicating the correct temperature.

Once the correct temperature is reached the case is completely quenched in water to stop the annealing process at the desired hardness.

Failing to keep the base of the case cool can anneal the case near the head, where it must remain hard to function properly.

Another approach is to immerse the case mouth in a molten alloy of lead that is at the desired annealing temperature for a few seconds, then quickly shake off the lead and quench the case.