I was talking with an older gentleman the other day about annealing brass. It's something I've never done but am considering. He told me that factory brass needs to be annealed but military brass does not because it has been annealed. Is that correct, or does brass need to be annealed periodically?

I was talking with an older gentleman the other day about annealing brass. It's something I've never done but am considering. He told me that factory brass needs to be annealed but military brass does not because it has been annealed. Is that correct, or does brass need to be annealed periodically?

A simple comparison is a piece of bailing wire. It takes considerable force to cut with wire cutters. If you bend it back and forth repeatedly in the same spot, it will become brittle then weaken and break.

The same thing happens with your brass. With each firing, pressure expands the neck and shoulder to the dimensions of the chamber. When we run it into the sizer we bend it back the other way. After fireforming, the shoulder should only move a few thousandths each way. The neck moves considerably more. It is for this reason that split necks are where brass will commonly fail with repeated firings. Before that starts happening, as your brass is repeatly fired and sized, it loses malleability. Neck tension of your cases becomes inconsistent. It may manifest as flyers or your groups may open up. This is telling you it is getting brittle. If you keep loading it, you will start getting split necks.
When you anneal, you relieve the stress in the metal and the malleability and consistency returns.

I anneal most of my brass every third firing. I shoot 300WM and 7RM a good bit. I anneal it every other firing.