Part 3a. The case, continued
Exact design and configuration of a case depends, in a large part, on the dimensional blue prints. There will, however, be internal differences depending on the thickness of the brass. Internal volume will vary greatly. Similar looking cases like .223 Remington and 5.56 X 45 may look the same on the outside but military rifle ammunition tends to have thicker cases to prevent blow ups in loose fitting (sometimes poorly maintained) fully-automatic weapons. Because of the thicker brass case, the military equivalent case requires less powder to achieve the same velocity. Consequently, the same powder charge used in a commercial case may be overloaded in a military case. Great care should be exercised when loading rifle cartridges that also have a military equivalent like .223, .308, .30-06. If a military grade case is mixed in with a batch of commercial cases, extreme pressures can result causing damage to the gun and shooter as well as bystanders.
There are lesser differences in volume between similar cases from different commercial makers and even differences between lots from the same manufacturers. A Remington case has a different thickness than a Federal case or a Winchester case. When preparing loads (especially near maximum loads) you should use only the case brand the load was originally developed in.
Accuracy fanatics segregate their cases by weight. Given that all the external dimensions are exactly the same, weight will determine which cases have the same internal volume. Many benchrest shooters will purchase a large lot of new cases from one manufacturer and then segregate them by weight. They will develop a load for a particular batch of brass from the lot and re-use the cases until they fail or risk failure because of too many repeated loadings. They then develop a new load using another batch of the brass, and so on.
Case life The number of times a case can be safely loaded depends on a number of variables such as the exact alloy of the brass, the amount and type of powder used in each round, the pressure of the load when fired and the manner the case is resized (standard, small base, collet or neck sized). Some high pressure magnum rifle cases might become suspect after 4 loadings. Some low pressure handgun cases may be perfectly serviceable after 10-15 loadings.
Who makes the best brass? This is a question many people ask. Some prefer Federal, but others believe Federal brass is too hard and has a limited life span. Some like Remington, but others will claim Remington brass is too soft and gouges easily by extractors and ejectors. Some swear by Winchester, but others claim Winchester brass is too inconsistent. Most agree that Norma makes the best brass but it is very expensive in comparison to domestic brass. Norma allegedly drills their flash holes rather than punching them out. This yields a consistent flash hole that helps with consistent ignition. If the flash holes are de-burred on the domestic cases they are probably as good as the Norma brass at a fraction of the cost.
Of course the brass must first be cleaned and polished before any of the above is started. Polishing should never be done with a product containing ammonia. Ammonia is very bad for brass. It can weaken the brass leading to a dangerous situation. There are several methods and products available to clean and polish brass. Vibratory tumblers are by far the most popular. For a media in the tumbler people use either ground corn cob or ground walnut hulls. Many people add a chemical polish to the media. These chemicals are available from RCBS, Lyman, Midway and Flitz. Some use an automotive finish restorer known as Nu-finish. There is a liquid case cleaner called Losso that does not require a vibratory machine.
Severely corroded brass, especially with green or crusty white spots should not be fired as it is potentially dangerous.