When we first solicited Pro Post topics, several requests came in for a piece on annealing. Now, I'd be the first to fess up to being an "ammo nut." I've been reloading for decades now, and I've always found the science of ammo very interesting.
Great shooting depends as much on the ammo as on the rifle shooting it.
That said, I've spent almost no time annealing my cases over the years. The only real exception is a batch of .308 brass reserved for a particular bolt gun of mine. Does that mean it's not worth your time? Not necessarily, but let's cover the basics first.
The standard brass case is a technically complex device that accomplishes a difficult task. It must be malleable enough to form exactly to the walls of the chamber during the firing process. This creates the tight seal between the case and chamber to prevent the high-pressure gasses from escaping and flooding the action.
At the same time, the case must be rigid enough to endure the pressure peak. Otherwise, the unsupported portion of the base might extrude into the bolt face or literally give way under the pressure.
To accomplish this balancing act, cases have alternately soft and hard areas. The base is significantly harder than the upper body, especially the neck and shoulder area. However, every time the case goes through a cycle of firing or reloading, these malleable areas become work-hardened. After enough cycles, the neck will crack.
Now, I have cases fired over a dozen times that have not had this failure. On the other hand, people have set records by annealing every reloading cycle for consistent neck tension on the projectile. There is no arguing that consistent internal ballistics are very dependent on neck tension.
The principle behind annealing is that by applying heat, the neck area is re-softened and the case "rejuvenated." Yes, it does work, and it does make a difference. But, there's more to it than that.
Before you getting involved in annealing, understand that it has its pitfalls. These range from just wasting your time to the possibility of catastrophic case failure due to improper technique. Some time back, the typical method for annealing was to place the cases base down in a pan with maybe an inch of water. Using a propane torch, you'd heat the upper part of the case until it changed color. As you can imagine, it was difficult to apply heat consistently over 360° doing it this way.
A better solution was to use of a variable speed drill. You'd spin a long socket wrench suitable to hold the case while applying the torch. Once it reached the appropriate temperature, you'd quench it in water. This method gave much better coverage but at the price of speed.
Thankfully, you can now buy a well-designed machine to handle multiple cases in an automated fashion. A BC automatic case annealer is the way to go if you really want to get into this. It provides a consistent result and virtually eliminates the possibility of botching the job.
The danger potential for annealing comes in over-annealing, and more so, in annealing the base. If you soften the base of your cases, they will no longer function as designed. They might rupture or split and release high-pressure gases into the action and ultimately into your face.
With careful technique, you can avoid such catastrophic failure. But the risk is always higher than a simple cracked neck when a case reaches the end of its life.
So, the final verdict...