Cartridge case annealing (techniques and equipment)

The Art and Science of Annealing is one of the best overviews that we found on the topic and well worth your time reading. You have probably encountered all sorts of information and opinion regarding annealing, so hopefully we can save you some time and confusion by explaining what works for us and why.

In a nutshell, here is what we have learned about annealing:

1. Method: Using a propane torch and something to spin the cases works just fine.  We personally know some excellent shooters who use this method. However, we found it to be slow and we wanted an approach that would guarantee absolute consistency.  We went with the Bench-Source machine, but there are other excellent machines on the market such as the Giraud.
2. Frequency:  Some shooters anneal every time while others choose a specific interval. We noticed work hardening around five firings that resulted in inconsistency in shoulder setback and neck tension, so we choose to anneal every three firings. Your mileage will vary depending on how hot your loads are and how aggressively you resize.
3. Temperature:  We use 750 degree Tempilaq applied inside the case neck to indicate that the proper temperature has been achieved. If you apply the Tempilaq outside the case neck you will not get a reliable indication of temperature as it will burn off instead of melting. If you turn off the lights, you will notice that the brass just barely starts to turn color when the desired temperature is reached. As you go beyond the 750 degree mark we observed that the flame will start to turn orange – you can see this with the lights on. From our research, we understand that this is the result of zinc burning off. We adjust the time on our machine between the point that the Tempilaq turns liquid and the flame starts to turn orange. In other words, if the flame is starting to turn orange reduce the time. Upon reviewing the close up shots of our video, we saw the slightest bit of orange (perhaps it was the camera being more sensitive than the human eye) so in hindsight we could have reduced the time by a quarter second or so. We let the cases air cool – we don’t quench them in water.
   1. Here is some additional information regarding the properties of cartridge brass. This reference shows the annealing temperature to be between  800-1400 degrees F. If that’s the case, why is 750 degree Tempilaq recommended? We spoke with one of the annealing machine manufacturers and they explained that the reaction time of a temperature measurement system will be slower than actual temperatures achieved for something as thin as a case neck. As a result, the indicated temperature will be exceeded. Higher temperatures could cause a separation of the zinc from the copper which further explains the flame turning orange when annealing time is extended past a certain point.
   2. Based on our research, a temperature between 750F and 800F will cause stress relief. We aim the flame at the neck/shoulder juncture. Some folks like to aim it at the neck and others the shoulder. When you see how the two flames meet and spread out vertically, it probably doesn’t make that much of a difference. Cases will turn color after annealing, but the degree of color change is not a reliable indicator. We have noticed that the appearance of cases will vary depending on brass manufacturer, brass lot, light source, and how long ago the case was annealed.
4. Observations:  We’ve noticed that the necks of annealed cases are never quite as soft as new cases, but they do get softer. Based on our research discussed above, this tells us that stress relief is still occuring. We could get them softer by increasing the heating time, but the flame turns orange indicating that zinc is burning off so we don’t do that. We can only surmise that brass must get heated to a higher temperature during manufacture. Heating to that extent once during manufacture probably doesn’t cause any harm, but to get that hot with each subsequent annealing will damage the brass. If any of our readers have insight as to how cases are annealed on an industrial scale please contact us. We welcome your thoughts and comments.