Neck sizing

[Half Dog]

I’ve been neck-sizing the brass for rifle rounds and I’m wondering how long the neck tension will hold. Has anyone seen test results to indicate how soon the neck tension relaxes enough to affect the rounds?

Thanks in advance for your time and effort.

I’m having trouble with clarity and I hope this helps express my question.
I’ve made several rounds by neck sizing and seating the bullets so they have .002” neck tension. I guess an exaggerated question could be; will the neck tension, on the bullet, relax to a point where it affects a shot group or will the tension remain for several years in storage on a completed round?

[M-Tecs]

Not specifically the answer you are looking for but this is as close as I think you will find. My understanding is cartridge brass does not age harden of soften.

I have 30/06 M72 match ammo from the 60's. I don't know if neck tension has changed at all but if it did it's not noticeable.

https://www.ampannealing.com/article...20time%20frame.

We then forwarded all the above to Derek Peterson. In response, we believe that Derek has provided us with a definitive article on the subject. He starts with an excellent explanation of work hardening and annealing, and then explains why correctly annealer brass will not age harden. He also explains what factors can cause brass deterioration over time.

Derek explains:

Brass is a unique metal in many ways. Strong enough to contain the explosion inside a rifle’s chamber, but soft enough to form to the chamber walls to prevent gas leak. When it comes to hardening and softening C260, or cartridge brass, there are only 3 factors that affect hardness. The factors are; #1 The amount of work done to the brass. #2 The amount of heat (temperature) applied to the brass. #3 The duration of time the brass remains at the elevated temperature.

With that said, the only way to make cartridge brass harder is to work it. Specifically, cold work. An example of cold work can be seen below in this graphic:




As mentioned above in the last paragraph, the amount of cold work / reduction is what makes brass harder. Specifically, what causes the brass to become harder after receiving cold work, has to do with the grain size in the brass. Cartridge brass receives its strength from the amount of grain boundaries contained in the particular sample you are testing. Basically, more grain boundaries equal stronger material, and/or higher tensile strength. Hardness and tensile strength are very closely tied, but not identical. Exactly how that is possible, I’m not sure of, but I have been told that on a few occasions by reputable industry professionals. However, with all of my testing, harder brass has equaled higher tensile strength.

The only exception to "cold work being the only way to increase brass hardness”, is during the annealing process of the cartridge brass. When you anneal brass, the brass actually goes through 3 phases. Recovery, Recrystallization, and finally Grain Growth. You can see the 3 phases below in the illustration:

Depending who you ask about this topic, the names of the phases might change, but regardless of the names used, there are only 3 phases.


Note: this illustration shows slow furnace annealing. "Flash” annealing the neck and shoulder of a case is much faster and at a higher temperature.





What you can see in the above graphic, is the 3 phases the metal goes through during the annealing process. When I say that the brass can get slightly harder during the annealing process, I am specifically talking about the recovery stage. Right at the beginning of the recovery stage, the duplex grains in the brass actually strengthen. This strengthening is what causes the tensile strength, and therefore hardness, to actually go up. This recovery stage only lasts for a short time, and its effects are erased when the temperature continues to rise. As the temperature continues to rise, the brass enters Re-crystallization, followed by Grain Growth, and subsequently begins to decrease in hardness. The temperature, very roughly, at which cartridge brass enters recovery, is around 500 – 550 degrees Fahrenheit. Or so I have been told, and the graphs I have studied illustrated.

The time needed, at the increased temperature, for the brass to enter the recovery stage, and therefore harden slightly, normally + 10HV, depends on the thickness of the metal. This is what I meant above when I said annealing depends on the temperature you anneal the brass at, and the amount of time the brass is allowed to anneal at that increased temperature. Generally speaking, higher temperatures require less time to reach the same hardness as a lower temperature for a longer time. However, generally speaking, brass heated to below 500 degrees Fahrenheit will not soften or harden regardless of the amount of time the brass is left at that increased temperature.

[garandsrus]

The necks do get work hardened by shooting and resizing, eventually resulting in necks splits. The brass can be annealed to reverse the work hardening and prevent splits. Some folks anneal each loading, and some never. I have some 6 PPC brass that I anneal when I feel the pressure vary when seating the bullet, probably every 5 to 10 loadings.