Turn up the temperature!By Matthew Cameron
- 6th Jun, 2020 Jun 6, 2020, 9:48 AM
- 0 Comments
Sometimes when the accuracy of a rifle diminishes, it takes time to work out exactly what the problem is. Often there may be several symptoms that are not the root cause of the problem. One of my own rifles (a stock standard factory Ruger 77V in .243 calibre Winchester) became involved in a series of tests that I was running for another article.
At the same time, another project was to test 55 grain Nosler ballistic tips in some new European brass. It was obvious that the usual suspects of loose screws, bad bedding and a rubbing barrel were not the culprits. Having eliminated the mechanics, the only other possible suspect was the ammunition.
I have always considered myself very fussy when it comes to ammunition; almost invariably case preparation is in excess of what is required. All powder charges are individually weighed, quality control on the reloading bench is best I can attain. However, something was certainly wrong.
In the end I had to revert to my reloading data records, all reloads are logged with the applicable details; it became immediately apparent that some of the .243 Winchester cases had crossed the reloading bench as many as seven or eight times.
The modern cartridge case, formed from strips of brass, is a wonderful piece of engineering. Containing pressures up to possibly 60,000 PSI only a few inches from your face when you pull the trigger it is the whole reason that a rifle can exist.
During the manufacturing process the brass is work hardened quite frequently and requires annealing to soften it up again, this situation occurs several times during the forming process.
“The modern cartridge case, formed from strips of brass, is a wonderful piece of engineering. Containing pressures up to possibly 60,000 PSI only a few inches from your face when you pull the trigger it is the whole reason that a rifle can exist.”
When new brass finally arrives at your reloading bench there is a graded difference in hardness from the base of the case to the mouth of the neck. Whilst the base must be hard the neck must be much softer.
It must not be too soft, otherwise it will collapse, perhaps the best word is that it must be ductile, that is, relatively soft but capable of being pliant at the same time. When the cartridge is fired the case expands under pressure in the rifles chamber, as this pressure reduces to ambient it springs back slightly to allow extraction.
A downside to this continual expansion and reduction is that the whole case begins to harden due to the constant working each time the rifle is fired, the hotter the load the more the case is affected.
The matter is compounded in relation to the neck and shoulders of the case when we de-prime and resize via the normal reloading dies, due to the thin neck the hardening process is particularly noticeable.
This is one reason why benchrest cases last much longer than conventional cases, the only part of the case that is worked using straight line reloading dies is the case neck, and then usually only several thousands of an inch.
“...some benchrest and long-range shooters have resorted to annealing case necks after every firing, they claim that the results speak for themselves.”
In addition, the tight chamber tolerances only allow minimum expansion of the case when the cartridge is fired. However, some benchrest and long-range shooters have resorted to annealing case necks after every firing, they claim that the results speak for themselves.
There are other reasons why case annealing may be useful, necking down cases in several stages may prevent an excessive number of failures. The same situation applies when a case is to be necked up to a larger calibre.
In addition, many cases for wildcat calibres require extensive forming. What then are the indications that the case is close to the stage when it either must be annealed or scrapped?
This is another reason for good reloading records, if you can extract the number of reloads for a certain batch of cases it is reasonable to predict when annealing or scrapping is approaching. In my experience primer pocket expansion will occur over time even with moderate loads.
If you use the same type of primers in a batch of cases, you will eventually notice a lack resistance when seating. You must be careful using this as an indication as different primers have slightly different diameters.
Normally I use up to seven different primers from five manufacturers; the variation in diameter is 0.007 inches. In any given case the largest may seat normally, the smallest would seat without much pressure. This is one reason why I personally prime using hand tools and not a large press, the hand tool has much more “feel”.
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Sometimes the first indication that this process is under way is the splitting of case necks. Using conventional decapping and sizing dies the resistance, or lack of it, as you withdraw a case over the expander ball can also indicate that there is a change in the brass composition.
Normally a good case with a ductile neck has some drag as the neck brass springs back, in a less ductile case this does not occur. In a similar fashion when seating a bullet if there is extraordinarily little resistance you should be suspicious.
WARNING: Whilst you need to hear the case neck it is IMPERETIVE that you DO NOT heat the base of the case to any degree. If you remove the hardness at the BASE of the case excessively you are creating a problem, there is no longer enough strength to contain the powder charge within the case when you pull the trigger.
There is a great deal of misinformation relating to the annealing process. The most often mentioned method is to stand the cases in a shallow pan of water and heat the neck with a propane torch until cherry red, at this point the case is knocked over into the water.
This process is not recommended for several reasons. Firstly, the heating of the case necks to a cherry red colour is incorrect and excessively hot, the neck is now much softer that what you require, and the brass structure has changed.
Secondly, using this method the heating of the neck is uneven; one side will be hotter than the other and this is unacceptable for the best results.
Many claim to have used this method for many years without any problems. There is a very narrow temperature band required to carry out the process correctly; you must manage this to achieve the best results.
The most effective temperature for our purposes is 349 to 351 degrees Celsius (660 to 665 degrees Fahrenheit), at this temperature the brass is a light blue colour. Immediately this temperature is achieved the whole case is immersed in cold water to reduce the accumulated heat as rapidly as possible, the requirement is to not go above 665 degrees Fahrenheit.
Thankfully, there is a method that allows this accurate temperature to be attained and not exceeded. Certain types of steel fabrication and welding have temperature limitations.
A US company has developed a stick or crayon with specific temperature limits, the item to be protected is marked; when the temperature is attained the mark simply becomes a liquid. Thus, for our purposes the stick at 649 degrees Fahrenheit is the closest to our requirements, they are exactly accurate.
“The most effective temperature for our purposes is 349 to 351 degrees Celsius (660 to 665 degrees Fahrenheit), at this temperature the brass is a light blue colour.”
Practical use of the stick immediately highlighted two problems. Firstly, I found it exceedingly difficult to get the stick to adhere to the polished brass, secondly the colour of both items is awfully close, preliminary short-term heating assists. However, despite these facts it was useful to ascertain the amount of time necessary in the tip of the blue flame.
The first part of the process is to polish the unprimed brass that you are going to anneal, this is necessary as you will not see the colour change on a dirty case.
The best method of applying a consistent heat distribution is to rotate the case in the tip of a high temperature flame; there are several methods of achieving this aim. The first method is an item that came from the local hardware store.
Named a “Claw pick-up tool” it has four small claws that may be extended via a plunger on one end of the tool, these four claws will grasp a case head and allow rotation in the flame by hand. It also will hold cases with small primer pockets; it cost less than $6.00.
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The second method used by the author is a Lee case trimmer locking stud and shell holder; this locks the case in position. The bottom of the lock stud fits in the jaws of an electric drill or screwdriver and when rotated allows even flame distribution.
You should note that you must purchase two separate packs to get the necessary items using this method. The first is a Case Length Gauge and Shell Holder and the second a Cutter and Lock Stud. As a bonus you get case trimming that is calibre specific. I chose .243 Was the case head covers multiple types of cases.
The next item we need to consider is safety; on a personal level we need eye protection and gloves. There should be flame retardant available (quenching bucket?) or a fire extinguisher; we must also ensure that there is nothing flammable in the immediate vicinity.
With all the tools assembled and some cases to practice on it was time to get to work, it makes sense to practice on several older cases first to get the technique and temperature correct. Applying the tip of the flame halfway up the neck and counting to seven, (approximately seven seconds) appears to work okay.
The most important portion of the case is junction of the body and the start of the shoulder. If you watch this area it will turn brown in about five seconds, rapidly followed by bronze and then blue, this is what we need to achieve. Note that the heating of the NECK is a product of both time and temperature, thus it must be heated very rapidly.
Quenching the case immediately should leave the light blue ring just below the case shoulder. In my opinion the annealing process is correct when this occurs. In addition, if the temperature is not excessive the case will retain its original shine even though the colour has changed, if absent the brass structure has changed due to overheating.
Personally, whilst I favour the drill mounted shell holder to rotate the cases in the flame, the claw tool is suitable for smaller cases; in addition, I did not have to purchase another shell holder. The results appeared to be similar.
After annealing cases you can remove the blue annealing marks by soaking cases in plain white vinegar for twenty or so minutes, dry them naturally and then tumble. Once again good reloading records are necessary.
Perhaps you might consider leaving the annealing marks on the necks as an indication that they have in fact passed through this process.
“Whilst annealing may extend the life of a batch of brass other issues may be the final arbitrator, eventually you will reach a stage when the largest of primers will no longer seat with any pressure.”
The inevitable question is how many times can brass be annealed? It is probably not possible to answer the question; there are simply too many variables. The only figure quoted was that one shooter had used his cases some 40 times without problems, they were apparently annealed often!
Whilst annealing may extend the life of a batch of brass other issues may be the final arbitrator, eventually you will reach a stage when the largest of primers will no longer seat with any pressure.
Hot loads will require case annealing more frequently. I find the process straight forward and have annealed several thousand cases successfully over a several year time frame.
I anneal every time a case crosses the reloading bench, this is personally simply a matter of logistics when dealing with multiple case types and only small numbers of cases at any one time.
Home guide to cartridge conversions: Nonte 1967
Designing & forming custom Cartridges: Howell 1995
Precision Shooting, November 1999, Wright.
Numerous internet sites.
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