On the softer side: cartridge case annealing.
Unless we stick way too much powder in our loads, expanding primer pockets beyond use, the biggest limitation in case life is the neck cracking due to work-hardening. Many metals become brittle and crack if "pushed" back and forth repeatedly, exactly what happens to brass after we resize and shoot it over and over again.
Work-hardening primarily affects the neck both because it's the thinnest part of the case, and because resizing works the neck more than the rest of the case. In typical bottleneck rifle dies the neck is first squeezed down when the brass is shoved into the die, then "bumped up" again by the expander ball on its way out of the die. Even when we only squeeze the neck smaller, with bushing or collet dies, the neck still gets worked more than the rest of the case, especially if we neck-size only. In time this makes the neck brittle, whereupon it cracks during resizing or firing, and the case is useless.
Workin' Too Hard
It's also a good idea to anneal the necks and even shoulders of wildcat cartridges after we neck cases up or down or blow the shoulders out. All case-forming techniques work-harden brass, something to consider after we've spent considerable time creating a batch of .223 Ackley Improved or 6.5-06 cases.
Luckily, it's easy to bring case necks back to life. Many techniques suggested for annealing, however, do almost as much harm as good.
For decades the technique usually suggested was to stand the cases in a pan full of water deep enough to cover all but the neck and shoulder of the case. The necks were then heated with a propane torch until they glowed red, then tipped over into the water. One problem with this method is it's difficult to heat the necks evenly. One side of the bullet exiting the neck may tilt slightly. Also, some necks end up softer than others. Neither problem helps accuracy.
Some descriptions of this technique suggest tipping the brass into the water is a necessary part of annealing, but the water merely prevents the casehead from being annealed. We want the case head to remain relatively hard; otherwise a normal load results in a blown case, and maybe a blown gun. With brass, air-cooling results in the same amount of annealing as water-quenching.
Also, heating brass really red-hot can make it too soft. Brass is a "substitutional alloy," meaning the atoms of the two elements have similar structures. Atoms of the lesser element (in this case zinc) are substituted for some of the copper atoms. Cartridge brass is about 70-percent copper and 30-percent zinc. Heating brass hot enough for the neck to appear red in normal light requires a temperature above zinc's melting point of 787 degrees Fahrenheit. This won't melt the brass, because its overall melting point is around 1,700 degrees F, but does make the brass softer than if heated to just below zinc's melting point. We want the brass pliable but not soft.
Brass will anneal at 600 degrees, but it takes an hour at that temperature. Typical annealing instead applies temperatures of around 725 to 750 degrees for a shorter period. The technique I've used for the past decade or so was developed by my friend Fred Barker, a retired metallurgist who published an article about it in Precision Shooting magazine. Fred knew the old torch-the-neck technique often resulted in overheating, and also thought it kind of a pain.
Instead of a torch, Fred used a simple paraffin candle. Believe it or not, the tip of a candle flame produces over 1,500 degrees F. By applying heat-paint that melts at 725 to 750 degrees to the neck of the case, Fred eventually found holding a typical rifle case about halfway up the body, then turning the neck in the tip of the candle-flame until the case grew too hot to hold, produced the right amount of annealing.
When the case gets too hot to hold, it's dropped on a wet towel and wiped off, both removing the soot from the candle flame and preventing heat from migrating to the head of the case. I generally use paper towels, tossing them when they get too dirty, but a cotton towel will do.
The Barker Technique is simple, cheap and quick, but perhaps not as precise as some nit-picky handloaders might desire. A couple of years ago Hornady brought out their case annealing kit, based on much the same principle. The kit includes three case holders with 1/4" shafts that fit into a typical power screwdriver or handheld electric drill, and a bottle of 475-degree Tempilac temperature-indicating liquid.
The case holders don't grip the case; instead the case just slides into the cylindrical hole in the middle of the aluminum holder. The case body is painted with a ring of Tempilac 1/4" down from the base of the shoulder, then, inserted into the case holder. Then the flame from a propane torch is applied to the case neck as the case spins slowly. The neck reaches 700+ degrees by the time the Tempilac, 1/4" below the shoulder, reaches 475. When the Tempilac melts, the case is dumped into cold water, perfectly annealed.
For those handloaders who need to anneal a big bunch of cases, Ken Light Manufacturing offers the BC 1000 Automatic Case Annealer. This features an electrically turned rotary head that holds up to 20 cases; as the head turns it brings each case neck in line with a propane torch, annealing 1,000 cases per hour. At $390 it isn't exactly cheap, but for those of us who do a lot of shooting it would soon pay for itself.
HORNADY MFG. CO.
3625 OLD POTASH HWY.
GRAND ISLAND, NE 68802
P.O. BOX 2745
HAVASU CITY, AZ 86405
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|Date:||Jun 1, 2010|
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