Annealing Brass Perfectly: Beginners Guide

If you are someone who hits the shooting range regularly, you must have heard about annealing your brass cartridges.

Annealing brass cartridges is necessary if you want to reuse your cartridges.

How is brass annealed?

Annealing brass is a process of heating the brass workpiece above its recrystallization temperature and then cooling it. This results in softening of brass and relieves any internal stresses developed in the material due to previous operations. Brass annealing is commonly done to soften bullet casings to reuse them.

This article discusses the process of annealing brass in detail and provides insights about annealing bullet casings.

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Annealing Brass: How is it Done?

Annealing Parameters	Optimal Conditions
Annealing Temperature	400–700 °C
Cooling Technique	Either at room temperature or quenching in water

Annealing is a heat treatment process that alters the physical and molecular properties of brass to enhance its workability and machinability.

Cold working of brass results in the hardening of the material and increases its brittleness, making it prone to cracking under load.

Annealing reorients the grain structure, rejuvenating the ductility of brass and making it suitable for further operations like shaping, stamping, or forming. 

It involves heating the workpiece to its annealing temperature and then cooling it to allow refined grain formation.

Unlike annealing of steel, which requires controlled cooling of the workpiece, annealing of brass can be done by allowing it to cool at room temperature or by quenching it in water.

This is because, annealing of non-ferrous metals like aluminum, copper, and brass does not require regulated cooling to facilitate grain growth.

This process can also be used to anneal wires. However, annealing brass is generally performed for reusing bullet cartridges.

In the case of annealing brass cartridges, the neck and shoulder of the cartridge are heated to around 400–700 °C and then allowed to cool at room temperature. 

Most people tend to throw out bullet cartridges but they are perfectly capable of being reloaded a couple more times if annealed properly. 

Annealing restores the material's malleability and prevents it from breaking or developing split necks when you reuse the cartridge.

Annealing Brass Cartridges at Home: DIY Method

Annealing brass cartridges require a blowtorch to heat the neck and the shoulder of the casing until they reach the annealing temperature.

However, you can use two blowtorches, placed on either side of the casing, to uniformly heat the casing and increase productivity by reducing cycle time.

When subjected to the flame, the casing should be rotated continuously to avoid heat spots, until it turns dull red.

After heating the casing, it is allowed to cool at room temperature.

You can see distinctive coloration, like a faded rainbow, in the neck and shoulder regions of the cartridge after it is annealed. 

Although a casing can be reused 3-4 times without the need for annealing, it is advised to anneal it before every reuse to avoid the risk of accidents and to get the best results.

Why is Brass Annealed? Common Reasons

Brass is one of those materials that become harder the more it is worked. Annealing of brass is performed in order to reverse the effects of work hardening and make it more formable. 

This process improves the strength of the metal and relieves the stresses caused due to the various hardening process like bending, drawing, etc. that make it more brittle. 

Annealing brass not only improves its malleability, ductility, and strength, but it also improves electrical conductivity and magnetic properties. 

Bullet cartridges are predominantly made of brass, and hence they become hard and brittle during the reloading process.

As a result, cartridges need to be regularly annealed to reuse them and extend their life. 

A reloading cycle has three main steps: case sizing, bullet seating, and shooting. This stretches and resizes the cartridge, work-hardening the brass. 

The hardened brass loses its malleability, and this can be dangerous when used in a controlled explosive environment like shooting. 

Hardening of the brass also causes the cartridges to have a non-uniform neck diameter and spring-back from the sizing die. The harder the brass, the greater the spring-back effect. This results in inaccuracies in the sizing of the cartridge. 

Annealing your cartridges properly after every reload, will get rid of the spring-back from the die and allow you to size all of your cartridges identically. 

This is why annealing brass becomes an important step to help extend its life, allowing you to reuse your cartridges and improve your accuracy of shooting.

Apart from that, if you want to reform larger cartridges into smaller cartridges, like making wildcat cartridges, you will need to anneal the brass to make it suitable for the forming process. 

When reforming, after you set the shoulder back on the case, the neck of the cartridge will bulk up due to the extra brass in the region. This region will then need to be annealed to seal the chamber properly.  

Things to Consider When Annealing Brass Cartridges

One of the foremost things that you need to remember is to anneal empty cartridges only. Never bring a primed bullet near fire or heat.

When annealing the bullet casing, make sure to anneal only the neck and shoulder regions of the cartridge. 

You should not anneal the body and base region of the cartridge casing, as this part has to take the full impact of the hammer in the rifle chamber. Hence, you should not soften this part of the cartridge. 

When you are annealing your brass, you should be careful that you don’t over-anneal it. Over-annealing the brass makes it unsuitable to be reloaded. 

You can do this by keeping an eye on the color change of the brass in the case of blow torch annealing. You should heat the brass right until it turns dull red and then allow it to cool. 

Another way to make sure that your brass has reached the right temperature is to use a heat-sensitive paint, like Tempilaq, that melts at a specific point, thus indicating to turn off the heat source.

Under-annealing doesn’t have any specific disadvantages, but you would not get the results that you are looking for and this might cause the cartridge to develop neck splits the next time it is reloaded. 

Final Thoughts

In conclusion, brass annealing is an effective way to make your cartridges last longer, increase the repeatability & reusability of the cartridges, and improve the accuracy of shooting. 

Cartridges can be annealed in several different ways like blow torch setups, induction annealers, molten salt baths, etc. Each method has its pros & cons and can provide varying levels of accuracy. 

When annealing, you should be careful not to heat the body and the base region of the cartridge. 

To prevent this, you can keep the cartridge dipped in water while you heat the neck and shoulder. The water will absorb the heat that migrates to the bottom and keep the rest of the cartridge cool. 

You should also avoid overheating your brass, as this can make the cartridge excessively soft and make it unsuitable and risky to be reloaded and fired.

Frequently Asked Questions (FAQ)

How does Induction Annealing work?

Induction annealing is a non-contact process of heating brass using eddy currents. The brass is suspended in a magnetic field and eddy currents are induced in the material. This method causes less heat migration to the base of the cartridge which is more common in the case of blow torches.

How long should I anneal my cartridge when using a blow torch?

When you are using a blow torch, you should anneal your cartridge until it reaches a dull-red color. If you overheat the neck and shoulder, they will turn bright, glowing red, which makes the brass too soft to be reused as bullet casing.

What is Salt Bath Annealing?

Salt bath annealing is the process of annealing your brass cartridges by dipping them in molten salt. The molten salt quickly heats the brass to the required temperature and anneals the shoulder and neck regions of the cartridge. This process, however, should be practiced with abundant safety and caution as the salt bath chamber is extremely hot and can easily cause severe skin burns. 

Why is brass best suited to make bullet cartridges?

Brass is best suited to make bullet cartridges because of its malleability and rigidity. It is strong enough to take the rigors of the reloading and shooting operations in the rifle chamber, while also being soft enough to be reformed.  Brass becomes harder the more it is worked, hence, it must be regularly annealed if you wish to reuse your cartridges.