Annealing Case Necks
Date: Aug 01 2006
Eventually, if we load brass cases often enough, the necks will crack, either during sizing or shooting. This is because the necks normally get more of a workout than any other part of the case. Normally the neck gets worked over twice: when it's pushed up into the die, and then when it's pulled back over the expander ball. Even a straight-sided case has the neck sized down first, then "belled" to allow easy seating of bullets. Either bottleneck or straight cases can also be crimped afterward, further leading to brittle necks. Brittle necks eventually crack.
The brittleness arises from work-hardening, which occurs when any metal is bent and rebent enough. It's the same thing that happens to a piece of wire that's bent back and forth rapidly; the metal grows harder, due to changes in the structure of the metal itself, and eventually breaks.
Necks tend to crack after about five firings and resizings of brass cases. These days you can buy some brass in bulk so cheaply that it might not pay to take the time to anneal the necks. Instead it's easier to just pack them down to the nearest recycling center, and use the money received to help buy new cases.
But if the cases are expensive, like those for the .416 Rigby, or you've made them for a wildcat rifle, whether by fire forming or resizing or both, it pays to anneal the necks and get another four to five firings out of them. This is especially true for rounds that operate at relatively low pressures, such as the .416 Rigby. It's standard pressures are around 35,000 psi, so the rest of the case holds up remarkably well. The neck is the only problem, especially at $2 a case.