Cartridge Case Annealing

Matthew Cameron shares with us another interesting article about cartridge case annealing. What are the benefits?

Applying case to flame-note change in brass colour

The modern cartridge case, formed from strips of brass, is a wonderful piece of engineering. Containing pressures up to possibly 60,000 PSI only a few inches from your face when you pull the trigger it is the whole reason that a rifle can exist. During the manufacturing process the brass is work hardened quite frequently and requires annealing to soften it up again, this situation occurs several times during the forming process.

When new brass finally arrives at your reloading bench there is a graded difference in hardness from the base of the case to the mouth of the neck. Whilst the base has to be hard the neck must be much softer. It must not be too soft, otherwise it will collapse, perhaps the best word is that it must be ductile, that is, relatively soft but capable of being pliant at the same time. When the cartridge is fired the case expands under pressure in the rifles chamber, as this pressure reduces to ambient it springs back slightly to allow extraction.

Claw tool and drill holding cases.

A down side to this continual expansion and reduction is that the whole case begins to harden due to the constant working each time the rifle is fired, the hotter the load the more the case is affected. The matter is compounded in relation to the neck and shoulders of the case when we de-prime and resize via the normal reloading dies, due to the thin neck the hardening process is particularly noticeable.

Sometimes the first indication that this process is under way is the splitting of case necks. Using conventional decapping and sizing dies the resistance, or lack of it, as you withdraw a case over the expander ball can also indicate that there is a change in the brass composition. Normally a good case with a ductile neck has some drag as the neck brass springs back, in a less ductile case this does not occur. In a similar fashion when seating a bullet if there is very little resistance you should be suspicious.

WARNING: Whilst you need to heat the case neck it is IMPERETIVE that you DO NOT heat the base of the case to any degree. If you remove the hardness at the BASE of the case excessively you are creating a problem, there is no longer enough strength to contain the powder charge within the case when you pull the trigger.

There is a great deal of misinformation relating to the annealing process. The first part of the process is to polish the unprimed brass that you are going to anneal, this is necessary as you will not see the colour change on a dirty case. The best method of applying a consistent heat distribution is to rotate the case in the tip of a high temperature flame; there are several methods of achieving this aim. The first method is an item that came from the local hardware store. Named a “Claw pick-up tool” it has four small claws that may be extended via a plunger on one end of the tool, these four claws will grasp a case head and allow rotation in the flame by hand. It also will hold cases with small primer pockets.

Correctly annealed .270 W cases

The second method used by the author is a Lee case trimmer locking stud and shell holder; this locks the case in position. The bottom of the lock stud fits in the jaws of an electric drill or screwdriver and when rotated allows even flame distribution. You should note that you have to purchase two separate packs to get the necessary items using this method. The first is a Case Length Gauge and Shell Holder and the second a Cutter and Lock Stud. As a bonus you get case trimming that is calibre specific. I chose .243 W as the case head covers multiple types of cases.

The next item we need to consider is safety; on a personal level we need eye protection and gloves. There should be flame retardant available (quenching bucket?) or a fire extinguisher; we must also ensure that there is nothing flammable in the immediate vicinity.

With all the tools assembled and some cases to practice on it was time to get to work, it makes sense to practice on several older cases first to get the technique and temperature correct. Applying the tip of the flame half way up the neck and counting to seven, (approximately seven seconds) appears to work okay. The most important portion of the case is junction of the body and the start of the shoulder. If you watch this area it will turn brown in about five seconds, rapidly followed by bronze and then blue, this is what we need to achieve. Note that the heating of the NECK is a product of both time and temperature, thus it must be heated very rapidly.

Factory annealed .243 W and self-annealed .308 (turned neck on the .243 W)

Quenching the case immediately should leave the light blue ring about 1mmj in size just below the case shoulder. In my opinion the annealing process is correct when this occurs. In addition if the temperature is not excessive the case will retain its original shine even though the colour has changed, if absent the brass structure has changed due to overheating.

The inevitable question is; how many times can brass be annealed? In reality it is probably not possible to answer the question; there are simply too many variables. The only figure quoted was that one shooter had used his cases some 40 times without problems, they were apparently annealed often!  Whilst annealing may extend the life of a particular batch of brass other issues may be the final arbitrator, eventually you will reach a stage when the largest of primers will no longer seat with any pressure. Hot loads will require case annealing more frequently. The author found the process straight forward and has annealed several thousand cases successfully over a several year time frame.

The author anneals every time a case crosses the reloading bench, this is personally simply a matter of logistics when dealing with multiple case types and only small numbers of cases at any one time.

Shoot safe

Matthew