THOUSANDS of shooters assemble their own live cartridges at home, and annealing parts of their brass cartridge cases is a core skill.
We've already looked at some "must know" aspects of metallurgy and a basic annealing technique (February 3 and 17). Now it's time to describe the Naramore method, a superior approach that offers more control than other ways.
Neck annealing is the most common task, so we'll use that as our example.
First, polish the neck and shoulder of each case to a full, bright shine. If the shoulder needs annealing too, as it will in some kinds of case forming, polish the upper part of the body as well.
Ensure that the work is well lit, but avoid direct sunlight. Diffused daylight is best. If the lighting isn't right, we cannot read the heat signs properly.
Use a gas torch with a small, hot, pointed flame. Play the flame on the upper half to two-thirds of the neck, from a horizontal direction. Repeat: horizontal.
Some means of rotating the case is advisable. Alternatively, move the flame evenly around the case neck.
While applying the flame, watch for colour changes in the case neck and, at the same time, monitor the state of the shine. As soon as the neck shows an extensive, light bluish suffusion without losing its shine, remove the flame. The key word is "extensive".
Timing is critical. This colour change should start within five to six seconds, and must not be allowed to remain extensive for more than five or six seconds.
The light, bluish suffusion says the brass has reached the ideal 400-500 deg. C and the maximum time of five to six seconds ensures important changes have taken place.
That is, the internal stresses caused by strain hardening have been relieved and the brass has recrystallised. Small, stress-free grains have replaced the old, distorted ones.
Loss of shine, however, is bad news. It means grain growth within the brass has begun, whereas we want the stress-free grains to stay small. Evidence of grain growth says the metal could be over-annealed or dead soft, or maybe even burnt.
Treated cases should be put aside for slow air cooling. No need to dunk the cases in water.
After the cases have cooled, study them closely and compare them with our photo (right).
Necks and shoulders should still be shiny, as shown by numbers 1 and 2 in our photo. The annealed zone (in this instance, the whole neck) should have a reddish-brown hue - see no. 3.
The lower edge of the annealed zone should display a bluish band (no. 4), not to be confused with the earlier bluish suffusion.
By comparing the uniformity of the colouration from case to case, we can gauge how uniformly they have been annealed - an important check.
