Optimal Case Temperatures for Successful Annealing
Brass is an excellent conductor of heat. A flame applied at any point on a case for a short time will cause the rest of the case to heat very quickly. There are several temperatures at which brass is affected. Also, the time the brass remains at a given temperature will have an effect. Brass which has been "work hardened" (sometimes referred to as "cold worked") is unaffected by temperatures (Fahrenheit) up to 482 degrees (F) regardless of the time it is left at this temperature. At about 495 degrees (F) some changes in grain structure begins to occur, although the brass remains about as hard as before--it would take a laboratory analysis to see the changes that take place at this temperature.
The trick is to heat the neck just to the point where the grain structure becomes sufficiently large enough to give the case a springy property, leaving the body changed but little, and the head of the case virtually unchanged.
If cases are heated to about 600 degrees (F) for one hour, they will be thoroughly annealed--head and body included. That is, they will be ruined. (For a temperature comparison, pure lead melts at 621.3 degrees F).
The critical time and temperature at which the grain structure reforms into something suitable for case necks is 662 degrees (F) for some 15 minutes. A higher temperature, say from 750 to 800 degrees, will do the same job in a few seconds. If brass is allowed to reach temperatures higher than this (regardless of the time), it will be made irretrievably and irrevocably too soft.
Brass will begin to glow a faint orange at about 950 degrees (F). Even if the heating is stopped at a couple of hundred degrees below this temperature, the damage has been done--it will be too soft. From this discussion we can see that there are four considerations concerning time and temperature:
1. Due to conduction, the amount of heat necessary to sufficiently anneal the case neck is great enough to ruin the rest of the case.
2. If the case necks are exposed to heat for a sufficient period of time, a lower temperature can be used.
3. The longer the case necks are exposed to heat, the greater the possibility that too much heat will be conducted into the body and head, thereby ruining the cases.
4. The higher the temperature, the less time the case necks will be exposed to heat, and there will be insufficient time for heat to be conducted into the body and head.
You can see that there are a couple of Catch-22s involved in this annealing business. On the one hand, the brass conducts heat quite rapidly, and a fairly high temperature with sufficient time must be attained to do the job. On the other hand, too much time cancels the effect, and we will be left with a case that is too soft and not suitable for anything but scrap. Obviously, there must be a solution; otherwise, not even the cartridge manufacturers could do it right.
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Over-Annealing and Under-Annealing
When cartridge brass is under-annealed, virtually nothing has changed. If your case necks have become work-hardened, they will remain work-hardened, You will not see any improvement in case life or in accuracy. You will assume (incorrectly) that annealing is a waste of time. (In this case, with under-annealed brass, it is.)
Over-annealing is certainly the worst condition, and can even be dangerous, as pointed out above. Over-annealing has two aspects: over-annealing of the case neck only, and any annealing of the lower half of the case. There is no particular danger to over-annealing the case necks, which is the usual result of standing the brass in water and heating the necks with a torch. All that will happen is that your accuracy will not improve, or it may become worse, and the cases may seem to be a little more sticky during extraction. Case life will be improved because the necks are soft--too soft. However, you will conclude that annealing is not what it is cracked-up to be, and may even be a waste of time.
Any annealing whatsoever of the cartridge base is over-annealing and is dangerous. This area of the brass must retain the properties it had when it left the factory. If it is made the least bit softer, let alone "dead" soft, the stage is set for another shooter's nightmare. At the very least, you may get a whiff of hot gas directed toward your face. At the worst, you can be seriously injured as your gun behaves more like a hand grenade than a firearm.
I once heard a tale of a gentleman who placed his brass on a cookie tray and placed the whole batch in an oven at 650 degrees for over an hour. He wasn't hurt--at least seriously. His attitude toward annealing is very negative.
Cartridge brass which has been annealed over its entire length will exhibit signs of excessive pressure even with moderate and reduced loads. Indeed, cases in this condition are subjected to excessive pressures. Any pressure is excessive. Head separation, incipient head separation, stuck or sticky cases, blown primers, swollen cases, swollen case heads, enlarged primer pockets (I mean REALLY enlarged), and just about every other sign of excessive pressure imaginable can occur with cases which have been annealed over their entire length.
Testing Cartridge Brass for Hardness and Softness
This is not a definitive test of case hardness; it is more of an illustration than anything else. It requires a pair of small Vise-Grips and a few bottle neck rifle cases in various conditions of use: a factory fresh empty case, two cases that have not split but have been fired many times, and a couple of extra cases to set the jaws of the Vice Grips.
Place one of the used cases base down in a shallow tray containing water up to the lower third of the case, and deliberately over-heat the case neck--bring it to a red heat.
Adjust the Vise-Grips until the jaws barely touch the case neck when they are fully closed. Then, Carefully adjust them to go a few thousands of an inch beyond that point. the jaws should close until you can just barely visibly detect that the case mouth is deformed when the Vise-Grips are closed.
Ordinary pliers are not good for this demonstration because it is too easy to go too far. Vise-Grips, on the other hand, have an adjustable limit to which they can be closed.
Squeeze the neck of the used, but un-annealed case. Note the pressure required. Also note that when the pressure is released, the case neck springs back to its original shape.
Squeeze the neck of the factory fresh case. Once again note that the case neck springs back to its original shape, and that it takes slightly less pressure to deform it than the un-annealed case.
Now, squeeze the annealed case. The pressure to deform it is markedly less and when it is released, the case mouth remains deformed--no spring.
One more test--stand the annealed case on a metal plate (no water over the base) and heat the upper half to a red heat. Hold the heat for a few seconds and then let it cool. Adjust the Vice-Grips so that they can put considerable squeeze on the head area and crush the annealed case. Now crush one of the normal used cases. The difference is dramatic. Don't test an over-annealed case in a gun just to see what happens--take my word for it, the results can be dangerous to life, limb and eye, not to mention the condition of the gun. Finally, crush all test cases so that they won't get mixed in with good brass.
If you are a chemist or a metallurgist and know how to do it, you can make some photomicrographs of sections taken from the various critical points of several cases for reference. Of coarse, you could have been out on the range having a good time instead of fussing with such things, but to each his own.
Preparing the Brass for Annealing
The brass does not require any special preparation before it can be annealed. However, you will need a few polished cases in order to determine the correct temperature. This is important if you want first class results. If your first batch of brass will be pistol brass, don't use plated cases for the testing. Plated cases anneal just fine, but you will not be able to see the color of the brass as it heats up under that shiny coating of nickel.
If you have a polisher, polish the brass before annealing it. If you do not have a polisher, use a little Brasso or other brass polish on a dozen or so cases Polish them about half way down the case by putting a little Brasso on a soft cloth and turning them by hand. If you have a polisher, I don't need to tell you how to polish the brass.
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Originally Posted by Smoke-um if you got-um
