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Testing neck tension and Quantitative information
nononsense
Member Posts: 10,928 ✭✭✭✭
There are at least two recent topics on this subject of neck sizing and neck tension so I thought that this little blurb would provide some impetus towards a discussion of neck sizing, techniques and thoughts about the aging and changing of neck tension. Do you bother to try to control neck tension and consistancy of the tension? Did you even know anything about the potential of neck tension changing with age?
"RELOADING TIP--Neck Tension vs. Time: We've learned that time (between neck-sizing operation and bullet seating) can have dramatic effects on neck tension. Controlling neck tension on your cases is a very, very important element of precision reloading. When neck tension is very uniform across all your brass, you'll see dramatic improvements in ES and SD, and your groups will shrink. Typically you'll also see fewer fliers. Right now, most reloaders attempt to control neck tension by using different sized neck bushings. This does, indeed, affect how hard the neck grips your bullets. However, James Phillips recently discovered that another critical factor is at work. He loaded two sets of 22 Dasher brass. Each had been sized with the SAME bushing, however the first group was sized two weeks before loading, whereas the second group was neck-sized just the day before. James noticed immediately that the bullet seating effort was not the same for both sets of cases--not even close. Using a K&M Arbor press equipped with the optional Bullet-Seating Force Gauge, James determined that over twice as much force was required to seat the bullets which had been neck-sized two weeks before. The dial read-out of seating force for the "older" cases was in the 60s, while the seating force for the recently-neck-sized cases was in the 20s. (These numbers correspond to pounds of force applied to the bullet). Conclusion? In the two weeks that had elapsed since neck-sizing, the necks continued to spring back (get tighter) and stiffen. Lesson learned: for match rounds, size ALL your cases at the same time. If you want to reduce neck tension, load immediately after sizing."
"RELOADING TIP--Neck Tension vs. Time: We've learned that time (between neck-sizing operation and bullet seating) can have dramatic effects on neck tension. Controlling neck tension on your cases is a very, very important element of precision reloading. When neck tension is very uniform across all your brass, you'll see dramatic improvements in ES and SD, and your groups will shrink. Typically you'll also see fewer fliers. Right now, most reloaders attempt to control neck tension by using different sized neck bushings. This does, indeed, affect how hard the neck grips your bullets. However, James Phillips recently discovered that another critical factor is at work. He loaded two sets of 22 Dasher brass. Each had been sized with the SAME bushing, however the first group was sized two weeks before loading, whereas the second group was neck-sized just the day before. James noticed immediately that the bullet seating effort was not the same for both sets of cases--not even close. Using a K&M Arbor press equipped with the optional Bullet-Seating Force Gauge, James determined that over twice as much force was required to seat the bullets which had been neck-sized two weeks before. The dial read-out of seating force for the "older" cases was in the 60s, while the seating force for the recently-neck-sized cases was in the 20s. (These numbers correspond to pounds of force applied to the bullet). Conclusion? In the two weeks that had elapsed since neck-sizing, the necks continued to spring back (get tighter) and stiffen. Lesson learned: for match rounds, size ALL your cases at the same time. If you want to reduce neck tension, load immediately after sizing."
Comments
But I do know that the more times a case is fired the more often neck tension will be a problem because of work hardening the brass.
One of the main reasons that I anneal my brass after usually 3 firings, and I have read that some people do it every time it was fired.
Gun control is hitting what your aiming at.
why chase the game when the bullet can get em from here?....
Got Balistics?
I'm not sure about the annealing portion yet and I haven't left sized cases unloaded for that long a period of time so I can't attest to James' information.
I'm going to have to set up some testing to see if this is indeed true for all of the situations that I get involved with during reloading. I'll run a control set of cases as well as leaving a set alone for at least two weeks before I attempt to seat any bullets. The measuring will have to be done with a set up that I can create because I'm not going to buy any more arbor presses just for this test. This may take a while also since I'm a tad busy right now. My thought was to see if anyone else had noticed a difference such as this while reloading and if so, what was the time delay or other circumstances that might have contributed to the change.
Best.
Gun control is hitting what your aiming at.
Nononsense, I have the K&M arbor press sitting right here if you have access to a "loaner" seating pressure guage[;)]
why chase the game when the bullet can get em from here?....
Got Balistics?
Just got back from an unsuccessful deer circling event...but that's another post on another forum I'm sure.
Anyhow, I thought I would weigh in with my limited metalurgy knowledge as we use it in aviation. What nononsense has said about high neck tension causing flyers makes sense. It would seem more so especially in the case of vertical stringing as case pressure control is given over to neck tension. I had to say I didn't think too much about it but it does make a tremendous amount of sense.
The cases are doing what we call age hardening. Every copper based or copper inclusive alloy does it. Copper alloys harden the most just with age. The way we beat that is to stick the metal in the freezer. We usually heat the metal to 900 deg.F,(AL based alloy) then immediately it goes into the icebox for the maximum annealing effect. Since those are aluminum alloys and brass melts between 1650-1725 F. I'm sure you would need to go hotter with the oven. However, I think the same principle would apply that, after annealing, if kept on ice for the duration between sizing and seating/firing the softness will be maintained better. Copper alloys will still harden in the cold, but much slower. -I hope that's a constructive addition to this post
We have the second amendment so that all the rest are secure....UNK>
we need to set up and run this test or different portions of it and share our data here for all the serious loaders.[8]
why chase the game when the bullet can get em from here?....
Got Balistics?
That's pretty much how we keep copper based alloys from hardening. This procedure is used in the aviation industry for aluminum alloys that use copper as the strengthening/hardening alloy(2000 series). This is also proven technology with bronze and brass.
When you pull this stuff out of the frezzer though you must keep it wrapped until it gets above 32F so you don't get frost all over the brass and have a water problem and therefore powder performance problems..or worse, corrosion problems.
If possible, seal your brass in dry ice as you anneal it. Then keep it sealed until above water freezing point. Or, make it a point to dry each case as they come out of thaw. Whichever is easiest.
(If you find any modern research on aviation materials you are more likely to find 5000, 6000, and 7000 series aluminum alloys that are extruded. This technology won't work with these newer alloys as 1. they have manganese, magnesium and other alloys that only work with heat treating once, and 2. They are extruded metals so they are not malleable enough to make sharp bends like the 2000 series are.)
We have the second amendment so that all the rest are secure....UNK>
I figure they would be out of the freezer for maybe 24hrs before being fired at the match.
why chase the game when the bullet can get em from here?....
Got Balistics?
Now, to give the most common instance in which we use this method is with 2017 rivets. I have had some batches stay good outside the freezer for two weeks some for a month but they do get harder from the time that you first get them. Most batches of rivets I've dealt with stay good in the freezer for up to two years. If they are anodized they last longer. So, if trying to formulate a comparison here all I can give is the relative percentages of copper in the brass vs. aluminum alloy 70% to >5%. What would need to be factored in here is the speed at which the brass age hardens. It seems to me that the brass hardens faster by far than do the lower copper percentage rivets. For that we would each need to do some testing at the relative temps at which we live. I imagine the higher the normal temps the faster the brass would age harden. So, if you didn't freeze the brass after annealing but kept it just above freezing in a cold cellar it might still keep longer than if kept up in a warm upstairs room. Where nononsense is at in AZ it might be a tad hotter.
Not to play my own devils advocate but I know of a few times that people have talked about getting Lapua brass in vs. Norma brass and saying that Norma was much softer. If there is a different chemical composition to help keep it annealed longer that could be a factor. Each test would have to be within lots of brass against themselves as thats the only way I can think of to campare how fast it hardens and help eliminate other factors.
We have the second amendment so that all the rest are secure....UNK>
why chase the game when the bullet can get em from here?....
Got Balistics?
ANNEALING AND NECK TENSION.... Uniform neck tension is another reason to anneal your case necks. Each time you neck size and then the expander ball opens the neck up to the correct diameter, the brass' yield strength increases. It is called strain hardening. As the yield stress increases, there is more spring-back (to a smaller neck ID) after the expander ball opens up the neck. This effect increases the neck tension. A new annealed neck will have less neck tension than a case that has been fired and neck sized a number of times. Cartridge brass is 70% copper and 30% zinc and its yield stress and strength is increased by cold working.
Annealed cartridge brass has a yield stress of 19,000 psi.
? hard cartridge brass has a yield stress of 40,000 psi.
? hard cartridge brass has a yield stress of 52,000 psi.
So the neck tension on a ? hard neck will be twice that of a freshly annealed neck. If your rifle's chamber neck clearance is large, then you could easily get to the ? hard condition in 5 or 6 reloading cycles. It would take more cycles if your chamber neck is close fitting.