January 22, 2024
A reader recently asked about some rifle brass he’d inherited. The mixture of new and fired cases was likely 40 to 60 years old, and he wondered if they were safe to load after he’d cleaned and inspected them.
In order to provide a more insightful answer than a simple “yes” or “no,” I did some research. It’s been 50+ years since my material science studies in college and nearly 15 years since I retired from my engineering career, but it was interesting to rediscover facts I’d forgotten and learn just how cartridge brass is made and what factors affect loading/reloading it.
First, “yellow” cartridge brass is not an exotic or complex material. Composed of approximately 70 percent copper and about 30 percent zinc (with a smidgen of lead and iron contaminants), the alloy formula was pretty much standardized by the German military in the 1880s. By the 1920s, the manufacturing processes were pretty well universally established. According to my research, U.S. manufacturers were the last to adopt annealing the case neck and shoulder to avoid premature stress/season cracking.
By then, the only negative factor affecting case life was the corrosive mercuric primers that ignited the propellant charge. They were still loaded in some military munitions until the early 1950s. In fact, my sources state that cartridge cases that were properly manufactured since then should be perfectly safe to load and fire indefinitely if properly stored.
But what about the “age hardening” factor? Surely, cartridge brass will deteriorate simply by getting older, right?
The experts I spoke with emphatically say, “No!” Cartridge cases that have not been exposed to certain chemicals or chemical fumes (usually containing ammonia) do not age harden. The terms “age” and “season” hardening of cartridge brass are often used interchangeably, but the latter term is more appropriate because it implies the detrimental effect of any improper storage and handling environments on cartridge brass.
I had an interesting experience when the .32 H&R Magnum was introduced more than 30 years ago. I acquired sample ammunition from Federal, and after firing a box of it, I discovered at least half of the cases were split lengthwise. I asked a fellow gun club member, who happened to be NASA Marshall Space Flight Center materials lab director, if he could determine the failure cause. The answer was stress corrosion cracking, which was likely caused by improperly annealing the case body combined with the lubricant applied to the swaged lead bullets. With loaded ammo, the resulting neck tension/stress can accelerate the occurrence of “season” cracking. And if it’s been stored in adverse conditions, it will likely fail/crack after some period of time or when fired. The only other ways the cartridge case can fail is by excessive “cold work” hardening without subsequent stress relieving or if the propellant was improperly manufactured and it corrodes the case from the inside.
The typical cartridge case manufacturing processes involve starting with a 70/30 brass cup that is subsequently cold formed by drawing it around a series of precision machined dies in multiple steps. Between each “draw” the in-process cylindrical tubes are washed and annealed. During the final draw operation, a special tool “pinch” trims the irregularly shaped tube mouths to the desired length.
The case at this point is still a cylinder with one end closed. Next it is “body” annealed to soften the cylinder to the desired hardness before the closed end of each tube is “headed.” A steel ram flattens the base and punches the primer pocket into the still-unfinished case. Another tool may also be used to final form the base shape, pierce the primer pocket to form the flash hole, and impress the caliber and manufacturer’s headstamp. Alternately, the flash hole is punched through the case head just prior to inserting the primer.
These impact steps “cold work” the brass, making it harder, and therefore stronger, by changing the alloy’s grain size and structure. They also create a circumferential bulge around the case head. The belt edge of a belted magnum case is also formed in this operation. The final case head configuration, including the belt cylinder, is achieved by a turning operation that cuts the extractor groove, which also forms the rim. After final trim-to-length, straight-walled brass is complete at this point; however, bottlenecked cases are subjected to additional final forming steps.
One or more precision dies are used to reshape the neck and case shoulder. This, in turn, further work-hardens the brass. A final annealing process is required to achieve the desired ductility to ensure the neck will securely hold the bullet in place and also immediately expand to seal the chamber when the round is fired.
The cartridge case hardness varies from 100 (Vickers scale) at the neck to 180 or more at the case head. This ensures that the expanding hot gases follow the bullet down the barrel and not back through the receiver into the shooter’s face. It also means the relatively unsupported case head is strong enough to not rupture and cause a similarly undesired effect.
So, the final answer is not a simple “no.” If the reader’s “old” brass is not obviously defective with neck or body cracks or other indications of incipient damage, then it can usually be reloaded safely—especially if it’s annealed after passing a careful visual inspection.