Case Preparation

Education on Case Preparation

It’s a good idea to clean cases to get dirt, grit and chunks off the outside of the cases. Bright n’ Shiny doesn’t hurt, but isn’t necessary. Clean brass cases are easier to inspect. Corncob is a better all-around media. Walnut has a shorter lifespan, is too abrasive to polish, and is best restricted to stained or tarnished cases. Use corncob for general cleaning and polishing. A vibratory cleaner is fastest for tumbling brass.

If you have a vibratory case cleaner, then you can safely tumble loaded ammo in plain corncob for about 10-15 minutes to remove case and bullet lube. We suggest not using any polishing additives containing ammonia, such as Brasso, as the ammonia weakens the brass cases.

For smokeless powder, there is no reason to clean primer pockets. It’s a waste of time and adds no quality. Current priming compounds are sufficiently clean burning that it isn’t a problem of residue to prevent primers from seating fully.

Do not deprime cases prior to cleaning with dry media. There’s not enough movement to clean the primer pockets and media gets caught in the flash hole. If not removed, media can cause misfires, failures to ignite powder, which isn’t any fun.

After the empty cases are clean, inspect the cases for defects which may render the cases unsafe to reload. Sometimes brass cases will develop cracks, there might be debris inside the case, which can include, but is not limited to, mud, spider webs, wasp nests, mystery brass, smaller-diameter cases stuck inside larger cases after tumbling. If you have picked up someone else’s empty cases, there may be empty cases that are not reloadable mixed in among the reloadable cases. Cases made of steel or aluminum are generally considered to be non-reloadable.

Straightwall cases, regardless of being fired in a revolver or a rifle, do not require trimming. Straightwall cases get shorter over time, not longer. With extensive use, cases can get uneven, but a separate crimp die will ameliorate this problem.

If loading a bottleneck rifle cartridge, cases may have to be trimmed to reduce their length. Upon firing, brass flows from the base of the case towards the mouth. You must measure the case length AFTER resizing to see if the case must be trimmed. Most bottleneck cartridges can be fired two or three times before trimming is necessary. On straightwall cases, since there is no restriction in front, they tend to get slightly shorter with reuse. This length reduction has no effect on the use of the brass. On tapered cases, such as .38-55 and .45-70, the light loads Cowboy Action Shooters typically employ do not develop enough pressure to cause the cases to stretch.


The primary reason to clean cases before reloading is to remove any dirt or grit from the exterior of the cases that might scratch the dies, or more importantly, the chamber of your firearm. You also want to make sure no debris, such as mud, dirt, insect nests or smaller cases are inside the case. The fact that the cases are bright and shiny has no effect on accuracy or reliability.

Since the early 1960s, no US-made ammunition has used corrosive primers. Current priming compounds do not leave enough residue in the primer pocket to cause problems seating a new primer. Don’t waste time and effort cleaning primer pockets.

There are two commonly used methods of cleaning cases, dry media and wet media. Dry media cleaning uses a mildly abrasive material, typically ground corncob or ground walnut shells in a vibrating bowl to clean and polish the cases. It typically takes 1-½ to 2 hours of vibration to clean and polish a batch of cases. Walnut is the more abrasive than corncob cleaning media, and is only recommended for use with cases that are stained or tarnished. Corncob is recommended for cleaning and polishing of most fired cases. Walnut is more brittle than corncob, and has a shorter lifespan. With both types of cleaning media it is recommended that a small amount of polish be added to them before you begin to clean cases. The polish aids in cleaning and polishing, and extends the life of the media.

Wet media cleaning takes more time, and has additional handling steps. The cases need to be deprimed first, so that no moisture gets trapped in the primer pockets. Wet media usually consists of small stainless steel pins in soapy water, in some sort of vibrating or rotating bowl. These scour both the inside and the outside of the cases to clean them. There are several disadvantages to wet cleaning. First, the cleaned cases must be rinsed, then dried before they can be loaded. Next, when ammunition is fired, the inside of the case acquires a light coating of carbon. When reloading, this light carbon coating acts as a lubricant, reducing the effort needed to extract the case mouth expander. Additionally, there is evidence that the stainless media work hardens the cartridge case, which causes case separations.


Before you begin reloading, you should always visually inspect your fired cases, removing the cases that are either not suitable for reloading or require additional processing before they can be reloaded. Defects or special conditions to look for, and separate from reloadable brass include:

• Cracks in case necks. Handgun cases can typically be reloaded 10-20 times before the case mouth cracks. Once it cracks, it is unsafe to reload and should be discarded. The lifespan of rifle cases is more variable. Cases fired in a semiautomatic or lever-action rifle typically have a shorter lifespan (5 or 6 reloadings) than cases fired in a bolt action or single shot rifle (8 or 9 reloadings).

• Berdan primed cases should be separated and discarded.

• Cases made from steel or aluminum should be separated and discarded.

• US military cartridge cases, which have crimped in Boxer primers. These cases must have the crimp removed prior to reloading, usually by swaging the primer pocket. (See 
"Swaging" below.)

• In some instances, the cartridge cases for one caliber are made using multiple sizes of primers. Most notably, .45 ACP is now made using both large and small pistol primers, by a variety of manufacturers. US commercial 7.62x39mm ammunition is also made with different sizes of primer pockets, depending upon the manufacturer. Back in the 1930s and 1940s some .357 Magnum and .38 Special cases were made to use large pistol primers. It is unusual to run across this type of cartridge cases anymore, but they do exist.

• For best accuracy, and when loading ammunition at the maximum pressure levels, cases should be sorted by brand. Not all cases have the same internal capacity. Powder charge weights that would be safe in one brand of brass could be an overload in another brand. Military rifle brass is usually 10 percent thicker than commercial rifle brass. Check your loading data to see what type of brass was used to develop the data. If commercial brass was used, you should reduce the starting load by 10 percent to prevent an overload. For best accuracy and most consistent velocity, use the same brand of brass when reloading.


When bottleneck and tapered cartridges are fired, brass flows inside the case from the base towards the neck. When this fired case is resized, the neck of the case increases in length. This does not occur in straight-wall cases to the same degree. Typically, after two or three firings, bottleneck and tapered cases will have stretched beyond the maximum allowable length, and they must be trimmed. Failure to do so can result in ammunition that won’t chamber, or increased pressures from the case being forced into the bullet.

Sporting Arms and Ammunition Manufacturers’ Institute (SAAMI creates and publishes industry standards for safety, interchangeability, reliability and quality) specifications recommend trimming cases back to .010” below the maximum case length. This typically allows 2-3 more firings before trimming is needed again. As long as the case length is under maximum, and not more than .020” below maximum, then minor variations in case length have no effect on accuracy or performance. Most trimmers will hold within .005-.006” variation from one case to the next.

After trimming, it is sometimes necessary to use a chamfering tool to deburr the inside and outside of the case mouth. The Dillon RT1500 Electric Case Trimmer outside deburrs the case mouth as it trims. If you are loading boat-tail bullets, no inside chamfering is necessary. It is recommended to chamfer the inside of the case mouth when loading flat-based bullets.


While US military cases are Boxer primed, they undergo an additional step during the manufacturing process generally not done to commercial ammunition. After the primer is seated, a special forming station forces brass from the case head over the edge of the primer. The reason for this is so that in an under-pressured cartridge, the primer won’t blow out of the primer pocket and cause a firearm malfunction. Primers are made of sheet brass, and will easily deform to push out past this crimp. However, the crimp interferes with seating the new primer. This crimp must be removed, most often by swaging, so that a new primer may be inserted into the case. Swaging is a one-time operation. Once cases have been swaged, they can be reprimed just like commercial cases.

Reusing military brass with crimped primer pockets can be a tedious task. The Dillon solution is a remarkably simple device that bolts to your bench and allows you to swage the primer pockets with speed and ease. The case is supported from the inside, so you won’t be tearing the rims off the brass. A tool steel, hardened swage rod (easy to change from large to small primers) simply rolls the crimp away. No reaming is necessary. Our unique compound cam leverage system assures not only ease of operation, but perfect alignment with each and every round. Sound simple? It is and it works. What’s more, it’s inexpensive. The Dillon Precision Super Swage 600 comes with large and small swage rods. 

As an alternative to the Super Swage 600, some Dillon Precision reloading equipment has the capability of swaging military primer pockets inline during the reloading process. The RL1100, Super 1050 and CP2000 – our dedicated case processing machine – all have our swaging equipment built into them.

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