“…it has become pretty well known that if such shells are drawn and left under stress they will sooner or later give way in storage, and that the giving away of drawn brass is invariably associated with corrosion of some kind. The cartridge manufacturers pretty generally recognize that it is necessary to draw the temper of the necks of shells and also of the hard bodies as well. I recently discussed this matter with an European cartridge manufacturer and found that it is common practice in Europe to draw the temper of cartridge shells.”Mr. W.H. Bassett, Technical Superintendant of the American Brass Company. Comment made in discussing a paper entitled The Failure of Structural Brasses1, September 1915.
This comment gives us a glimpse back to a time when the world’s munitions manfacturers were on the cusp of solving a problem that had been giving them significant grief for some time, a problem then known as “season cracking”.
Early references to season cracking appear in available literature from E.S. Sperry of Connecticut2 and Diegel of Germany3. Sperry discussed mostly cracks found in seamless tubing while Diegel was focused on drawn rods. Both noted that cracking did not occur in hot worked material, and Sperry noted further that cold worked tubes did not crack in areas where the tube had experienced brazing heat upon installation.
A landmark lecture by Dr. E. Heyn of Berlin recounted a method he had developed for quantifying residual strain in a cold formed brass bar4. He demonstrated that a full anneal that produced recrystallization of the alloy completely removed the internal stresses, but also showed results suggesting that a lower temperature anneal could greatly reduce the residual stresses resulting from cold work without significantly affecting the physical strength increase produced by that same cold work. Heyn also pointed out that while season cracking was well known to be associated with severe internal stresses, it also seemed to require a external influence in order to occur, and he offered that one or more of applied stresses, mechanical damage, or corrosion damage were likely culprits.
Thereafter followed a flurry of papers and presentations wherein researchers expanded on Dr. Heyn’s findings regarding internal stress, cold worked hardness, and the effects of a wide variety of heat treatments, all with respect to copper alloys. Among the more notable: E. Jonson built upon his previous work and showed that ammonia was uniquely potent in producing cracking failures in stressed brass5; Mathewson and Philips clarified that the three principal variables in annealing were temperature, time, and the amount of cold work present in the material6; Merica and Woodward demonstrated that annealing at 300-400°C would quickly relieve internal stresses in cold worked bronze bars without lowering the strength, while annealing at 600°C would quickly lower both stresses and strength7. Annealing techniques used in these studies generally involved air ovens and times from 15 minutes up to several hours, however in discussion of the latter paper a participant member named M. A. de Forest, whose interests seemed to revolve around artillery shells, stated he had done some experiments with exposure times of as little as two minutes by immersing samples in a mixture of molten nitrate salts.
Eventually enough data had been gathered that Moore et al. were able to publish a definitive paper that fully outlined the major contributors to season cracking8. This included an anecdote wherein large quanitites of brass rods had cracked due to trace ammonia vapours that came from a wood stove burning sap wood in a warehouse.
The world took notice of these findings, and national armouries began the process of introducing a final mouth anneal to their cartridge cases, eliminating cracking of case necks in storage as a major logistical problem. Years later, in answering a question to a reader regarding neck cracks in World War I era ammunition, E.H. Harrison identified the reader’s issue as season cracking, and wrote “Ammunition loaded in the World War I period and shortly after is most likely to show this defect. It was accentuated in .30-06 military ammunition intended for rifle use by the fact the brass was annealed quite hard to permit easy operation of the Springfield rifle bolt. So much has now been learned of the manufacture of cartridge brass and cartridge cases that season cracking is, practically speaking, a thing of the past”9.
(I will comment here that Harrison’s use of the term “season cracking” in 1957 was rather quaint. By 1919 the researchers that were studying the issue were openly shying away from the phrase. They had learned that stresses and a corrosive environment were the critical factors, and also that the general mechanisms affected far more materials than just brass. In Europe academics were referring to the issue as stress cracking, while Americans were calling it corrosion cracking. By World War II those terms were merged and the study of stress-corrosion cracking (SCC) was underway in earnest, and continues to this day. SCC is probably the second most destructive corrosion mechanism extant, after general wastage, and affects engineering projects from space launches to deep burial of nuclear wastes.)
This then was the evolution of annealing in cartridge factories. But what of annealing for the handloader? With neither millions of dollars of industrial production nor the national security of nations at stake, significantly less academic attention has been paid to the question of annealing at home. And it is a very different question than was faced by the armouries of the world, for the simple reason that we reuse our brass, over and over again.
Despite the relative lack of careful study by great minds with large budgets, handloaders have been familiar with annealing for many decades. The earliest reference I have found thus far was a question from a reader to The American Rifleman. The reader had formed some wildcat cases from standard factory ones, and was looking for advice on how to anneal the necks. It was suggested he stand the cases up in a shallow pan partially filled with water, heat with a blowtorch, then knock each case over while red hot, stating that would make the neck “dead soft”10. He was cautioned that it was very easy to ruin cases by annealing, and suggested that if the reader was experiencing neck splits it may be the result of “inferior brass”, or his dies may have been working the necks excessively.
In fact, many of the earlier references to home annealing I can find take a similarly dim view of the process. Ken Waters, in a column on adapting new brass to obsolete calibers said “I don’t advise attempting to anneal the necks of reformed brass. In most cases it is unnecessary, and when it is to be done had best be left to a gunsmith or machinist who understands annealing”11. Harrison, responding to another question about neck cracks, argued that “Neck annealing is seldom worth the bother even where equipment is available”12.
Despite these discouraging takes, annealing seems to have remained in the consciousness of handloaders. Hill and Waugh did an article on ultra-light cast bullet loads in rifles, and suggested that annealing necks of brass dedicated to light loads could help with obturation at low pressures13. As far as technique the article is short on specifics, stating simply that “this is done by holding the necks in a gas flame for a few seconds and quenching them in water”.
Dresser presented an article entitled Case Neck Annealing which actually opens with the statement that “Annealing necks of commercial cartridges cases to be reloaded is seldom necessary”14. However it goes on to point out that brass is sometimes “drastically” reformed to new calibers, and that “unless given some anneal, such cold-worked brass is certain to have a short useful life”. He then presents a technique for annealing that will be very familiar to the modern reloader, namely rotating the case in his fingers while holding it in the flame of a propane torch, checking temperature with an indicating crayon until finally dropping it into a bucket of quench water. He states he likes to work with 700°F (371°C) crayons, and also mentions a temperature indicating lacquer known as Tempilaq as an alternative. This is the earliest home annealing technique I have found that includes a quantifiable method of controlling the process, and the earliest suggestion of a target temperature. Despite these milestones, Dresser’s opinion was that “It is quite unnecessary or of questionable desirability with many minor case reformings, and may do more harm than good if unnecessarily or incorrectly applied”.
Another article, this time in Handloader magazine, described work hardening of the brass as the most common problem resulting from conversion of standard cases to wildcats15. Annealing was recommended as a treatment for the “brittle” brass, with the explanation that it “greatly reduces case neck and shoulder defects”. The recommended practice is again the shallow pan partially filled with water, a gas torch (propane being adequate, but the author preferred oxyacetylene), with the addition of a hand held heat shield made of sheet metal with a hole in it that the user held around the midlength of the case to keep the flame from impinging directly on the case body. Notable is the control technique of setting a low blue flame and applying it to the neck for “approximately 35 seconds or until case necks discolour – and no longer!” At the proper time, the reader is directed to tip the cases into the water. The time is probably a printing error, as 35 seconds under an oxyacetylene flame seems unlikely to leave a case worth reloading, while 3-5 seconds might be about right.
As years passed, the idea that annealing may have an impact on the service life of more common cartridge cases began to take hold. Ross Seyfried wrote in an article about loading for wildcat cartridges that “Annealing should usually be used whenever you expand or blow out cases by fireforming. It is also a useful way to increase the life of any cartridge that you intend to reload often”16. Seyfried espoused the familiar strategy of standing the cases in a shallow pan of water and heating the necks with a propane torch “until you see the case’s colour change to that of the military rounds, or until the neck and shoulder have a dull red glow”. He makes no mention of tipping the cases over into the water.
In the internet era, John Barsness has promoted annealing to extend the life of common caliber cases17. He states that case necks can be expected to show cracks after about five firings, and that annealing before cracks appear will allow an additional four or five firings. He argues that the traditional shallow pan with water and heating to red hot method produces necks that are too soft and may collapse in bullet seating, so he advocates for hand spinning the case neck in the flame of a common wax candle for about 10 seconds. Barsness attributes this technique to Fred Barker. In the first part of the article, Barsness describes a liquid quench as an integral part of the annealing process, but in later describing his own technique, states he drops the hot cases onto a wet towel. He offers no explanation for this apparent discrepancy.
Ken Howell wrote that “Case necks, shoulders, and sometimes their upper bodies often have to be annealed before the case gets drastically modified”18. Howell recommended spinning cases to be annealed in an electric drill, and heating with a gas torch. “When the brass around the mouth reaches a temperature of about 660° to 665° Fahrenheit, its surface becomes light blue – and this is as hot as you want it to get…If you let the case get red, it’s a goner.” He recommended the use of temperature indicating crayons to achieve this target temperature, and a quench into cold water.
Damon Cali posted to BisonBallistics.com “if you work harden a brass (case) enough, you will make it so hard and brittle that it will no longer be able to stretch enough to reach the support of the chamber without reaching its failure point. The result is split necks…If heat is applied to a work hardened area of brass, the energy of that heat will cause the grain size of the metal to grow. As this happens, the material loses strength (it gets softer) and regains its tolerance for stretching without breaking. It’s a fully reversible process”19. Cali gives a temperature range of 650 to 700°F for this transformation, and states that at application of higher temperatures “the brass will get even softer, but not dramatically so”. He also makes a point of saying that cooling rates are unimportant in the annealing of brass, and that “you can cool it as slowly or as quickly as you like”.
Ken Light produced an article that has been reproduced on a couple of websites, and is well regarded as a source of information for the handloader. The claim is made that annealing can “make the brass last up to 10 times longer, but it will tighten up those groups too” 20 (it should be pointed out that Mr. Light was promoting an automated annealing machine of his own design at the time he wrote this article). The article also provides some detailed breakdown of annealing temperatures, including the following statements:
- “brass which has been work hardened is unaffected by tempertures up to 482°F regardless of time”
- “At about 495°F some changes in grain structure begins to occur, although the brass remains about as hard as before”
- “If cases are heated to about 600°F for one hour, they will be thoroughly annealed, head and body included. That is, they will be ruined.”
- “The critical time and temperature at which the grain structure reforms into something suitable for case necks is 662°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”.
Light also states that cooling rate does not affect the outcome of the annealing process.
For all of this growth in appreciation of annealing, doubters remain. The Lyman Products Corporation has published an article that says “Case necks will eventually become work hardened and begin to split…Some sources suggest that case life can be lengthened by annealing the neck…It is almost impossible for the reloader to control and maintain the precise temperature required for proper annealing. Therefore Lyman cautions against attempts to anneal case necks”21. And Stevenson, in a dissertation written in support of a masters of engineering degree, found that the annealing process used by a ranking competitive UK target shooter “produced very variable results…In some cases large variations were observed between two sides of the same cartridge sample”22. He went on to surmise that the simplest solution would be to simply drop annealing from the reloading process.
Gary Chambers, P.Eng. June 26, 2019
I would very much
appreciate hearing of other historical references to cartridge case annealing,
by factories and arsenals as well as by handloaders. Write ups that mention specific benefits, or
that are backed up by experiments, test data or credible references, are
especially sought after.
1- The Failure of Structural Brasses, P.D. Merica and R.W. Woodward, Transactions of the American Institute of Metals, Vol.9 (1915), p. 298
2- The Season-Cracking of Brass and Bronze Tubing, E.S. Sperry, The Brass World and Plater’s Guide, Vol.2 (1906), p.39
3- Nachträgliches Reissen Kaltverdichteter Kupferlegieungen, C. Diegel, Verh. d. Ver. z. Bef. d. Gewerbefleisses, Vol. 85, p.177 (1906)
4- Internal Strains in Cold-Wrought Metals, And Some Troubles Caused Thereby, Dr. E. Heyn, The Journal of the Institute of Metals, Vol.12, No. 2 (1914), p.3
5- Fatigue of Copper Alloys, E. Jonson, Proceedings of the American Society for Testing Materials, Vol.15 (1915), p.102
6- Recrystallization of Cold-Worked Alpha Brass on Annealing, C.H. Mathewson and A. Phillips, Transactions of the American Institute of Mining Engineers, Vol. 54 (1916), p.608
7- Initial Stress and Corrosion Cracking, P.D. Merica and R.W. Woodward, Transactions of the American Institute of Metals, Vol. 9 (1916), p.165
8- The Season-Cracking of Brass and Other Copper Alloys, H. Moore, S. Beckinsale, and C.E. Mallinson, Journal of the Institute of Metals, Vol.25 (1921), p.35
9- E.H. Harrison, Questions & Answers in Dope Bag feature of The American Rifleman, Nov. 1957, p. 89
10- L.R. Wallack, Questions & Answers in Dope Bag feature of The American Rifleman, Oct. 1952
11- Old Cartridges From New, K.L. Waters, The American Rifleman, Feb. 1957, p.37
12- E.H. Harrison, Questions & Answers in Dope Bag feature of The American Rifleman, July 1962, p. 86
13- Ultra-Light Rifle Loads, W.E. Hill and T.C. Waugh, The American Rifleman, Nov. 1961, p. 36
14- Case Neck Annealing, W. Dresser, The American Rifleman, Sept. 1962, p. 42
15- Annealing and Fire-Forming, N.E. Johnson, Handloader Magazine, May 1972, p.42
16- The Care & Feeding of a Wildcat, R. Seyfried, Guns & Ammo, Mar. 1989, p.78
17- Annealing Case Necks, J. Barsness, posted to https://loaddata.com/Article/BenchTopics/Annealing-Case-Necks/45, retrieved June 2019
18- Designing and Forming Custom Cartridges, K. Howell, Precision Shooting Inc. (1995). Chapter on annealing reprinted online at https://www.24hourcampfire.com/annealing.html, retrieved June, 2019
19- The Science of Cartridge Brass Annealing, D. Cali, posted to https://bisonballistics.com/articles/the-science-of-cartridge-brass-annealing with date stamp May 24, 2013. Retrieved June, 2019.
20- Cartridge Case Annealing with the BC-1000 Annealer- When, Why, How and If To Anneal, K. Light, posted to https://bkceng.com/kenlight/howtoanneal.html, retrieved June, 2019. Essentially identical versions of this article were posted to www.lasc.us, and www.6mmBR.com.
21- Reloading Handbook, 48th Ed, Lyman Products Corporation, 2002
22- Characterisation Study of Brass Cartridges For High End Competition Target Shooting, R. Stevenson, University of Strathclyde Engineering (2014)