The importance of cleaning brass

When cases are fired and ejected, they usually have two types of dirt on them - residue from the firing of the powder charge and dirt from the ground they land on. The powder residue can be seen on both the inside and the outside of each case, while dirt from the ground is usually only on the outside. If this dirt and grit gets into your resizing die, or the chamber of your gun, it can clog it up and can also scratch the cases.

Initial cleaning methods
When you get your fired brass home there are several ways to clean it, and each method has its pros and cons.
If you are cleaning just a few cases, then you can simply wipe them over with a piece of coarse material, like old denim, to remove the dirt on the outside of the brass. The inside of the necks can be cleaned with a piece of cloth wrapped around the end of a pencil or screwdriver. For stubborn powder residue, you can soak the cloth with a little bit of gun cleaning fluid.
A case cleaning tumbler will vibrate the cases inside a drum that contains some form of course media, typically ground walnut shell, and this cleans both the inside and outside of the case. You can also add polishing fluid to the media to help bring your cases up shiny, like new. With this type of cleaner, it is important to change the media regularly because it does wear, causing the granules to become rounded off and less effective over time.
There are also case cleaners that use very small stainless-steel pins and cleaning fluid in a rotating drum to clean brass. However, separating the pins from the cases and then drying the cases out fully is time-consuming.
Ultrasonic case cleaners use ultrasonic waves and chemicals in a fluid-filled bath to detach dirt particles from the brass, and they are extremely effective at cleaning all surfaces. Cases cleaned by this method also need drying off after cleaning.
All of these methods will clean cases effectively and get the ‘range dirt’ off. Whichever method you use, cleaning your cases as soon as possible after firing is a good idea, as the dirt comes off much more easily the sooner you get to it. If you leave it for a few days, the dirt can be much harder to shift.

Second clean
When cleaned cases are full-length resized, it is necessary to lubricate them to reduce the friction between the brass and the die, both on the outside of the body and the inside of the neck. Whatever type of lubricant you use, it will require removing once you have finished sizing the cases, and this is a step that a lot of reloaders tend to neglect.
If you do not remove the case resizing lubricant, then it can cause a few issues. Firstly, it can make the cases tacky, and if dirt or grit sticks to them, it will get into the chamber of your gun where it can build up and may damage the cases when they are fired. Secondly, it can affect the way that the brass moves in the chamber when the ammunition is fired. With no friction between the outside of the case and the chamber, because of the presence of case lubricant, a greater amount of the chamber pressure will act to cause the case to expand more lengthways. This will increase the likelihood of accelerated case wear, potentially causing case head separation. Under normal circumstances, with no lubricant on the outside of the cases, the brass will expand and grip the inside of the chamber wall, sealing correctly and preventing gases from escaping around the outside of the brass. If lubricant is still present, then the grip is reduced, and chamber pressure can be lost.
The quickest and easiest way to remove sizing lubricant from your brass is to simply wipe each case with a rag, paper towel, or a piece of old denim. If you have resized a lot of cases, you can put them through your case cleaner again, saving some time. However, if you are using one of the ‘wet’ cleaners, you may find that drying them all again is just as time-consuming as wiping each one.

Case mouth cleaning
It is also very important to remove any case lubricant from the inside of the case mouth, whether it be excess lubricant from the outside of the case that has got there accidentally, or case mouth lubricant specifically put there. When full-length sizing with some dies, the inside of the case mouth is lubricated to ease the expander ball’s travel through the case mouth and avoid excessive stretching of the brass in this area. If that lubricant is not fully removed, it will reduce the effectiveness of the case neck tension, meaning the case will not grip the bullet properly. If this happens, then when the powder charge is ignited, the bullet will start to move out of the case before the chamber pressure has reached the correct level. Inconsistent chamber pressures and muzzle velocities are often caused by lubricant left in the case mouths.

Conclusion
Case cleaning is important in terms of both the consistency of your ammunition and the life expectancy of your brass. It can be time-consuming, but if you use one of the various case-cleaning machines available, you can get through a large number of cases in a relatively short time. The second clean, and particularly the cleaning of the inside of the case mouth, is often not given the attention it needs, even though it does affect the quality of your ammunition, making it well worth doing. If you are applying an additional crimp to your ammunition, to overcome consistency issues, it is well worth trying to clean the inside of your case mouths more effectively instead. If nothing else, clean and shiny ammunition looks so much better than dirty stuff!