- March 6, 2016 at 4:37 pm #25538dvernaParticipant
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Doc’s post on the annealing machine was interesting. While many anneal cases to extend case life, it will also affect neck tension. The question becomes “how important is neck tension in achieving accuracy?”
We have seen how a cast bullet can be sized by too much case neck tension. That is an extreme situation and not what we need to dwell on as it is easily determined and corrected. Assuming the bullet is not deformed on seating, how does neck tension affect accuracy? Neck tension affects the force required to move the bullet out of the case. This affects chamber pressure and ultimately velocity. Thus, variations in neck tension should affect ES and SD of velocity readings – which may result in more vertical stringing of groups. Does that make sense? So if our groups are round, and we have low ES and SD, can we rule out neck tension as a significant factor?
I understand that the force to move the bullet will also be dependent on other factors. Seating depth, neck length, surface condition of the neck and bullet, lube used, etc. It will also be affected by the pre-load. This pre-load is determined by both the amount of expansion the bullet causes on the neck ( .001″, .002″, etc) and the condition of the case neck material. A thin neck will expand more easily as will a softer one.
Assuming the rifle and shooter are capable, accuracy is dependent on the both the load the rifle “likes” and the consistency of that load. For cast, finding the right bullet and lube are the challenges. The bullet must not only fit but needs to be of a proper alloy and cast VERY well. It seems to me that neck tension is a minor factor in achieving accuracy – at least in the cast bullet world. It may be more important to have uniform case walls so the bullet is seated as concentricly as possible than expending the effort to anneal.
Now, if someone is chasing bug holes with bench rest rifles, everything one can do to reduce variability may be justified. But if you cannot get a load to shoot with once fired brass that has been properly prepped, I doubt annealing will makes a difference.
- March 6, 2016 at 6:04 pm #25543VANNParticipant
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I’ve seen noticeable differences in the same load before and after annealing. Just an extreme example is my 7MM Ultra Mag. On my second reloading I noticed accuracy falling off big time, on closer examination I found that I could actually rotate the seated bullet in the case. Now I anneal my Ultra Mag brass before sizing every time.
With my 338 Win I found that I get best case life and accuracy if I anneal my brass every 5 firings. I have been able to stretch my case life dramatically by doing this.
I have some 308 cases that have been loaded over 25 times by simply annealing them all after the first sign of a split neck on one case.
To be honest I don’t think of my self as a really good shot, not in the likes of the other members of this forum. I do however put a lot of rounds down range.
After annealing it seems to me that it takes one or two reloadings for the tension to get back right and accuracy to settle back in a few of my rifles.
- March 6, 2016 at 7:05 pm #25545GoodsteelKeymaster
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To the question: How important is neck tension to achieving “accuracy”?
Answer: Not much.
If your rifle is correctly built, you will be able to shoot less than 1″ @ 100 and all that is required is that your brass be of decent mainstream manufacture, and that you know how to load good ammunition.
Now, If you are more correctly asking “how important is neck tension to refining accuracy?”
This assumes you have already gotten the circus out of your rifle’s front lawn, scraped the pizza off the ceiling, patched the holes in the walls, painted, hung drapes, and have your best easy chair set up in the living room with a glass of 100 year old scotch sitting on the table beside you. (figuratively speaking).
Once you have a rifle that is actually capable of sub MOA accuracy for ten shots (very rare in my opinion), with no more of these games: Oops I missed. Oops, those were all called fliers. Oops, that was the wind. Oops, oops oops oops etc etc etc etc. I’m saying when you have a rifle that gave you 1.25″ for ten shots on it’s worst day, and .75 on its best day, and you call the average 1MOA, and your really want to be able to cut that in half………then yeah, Neck tension becomes one of the things you look really hard at.
I’m pretty sure DocHighwall is at that point.
If you’re not at that point, then worrying about the enth degree of neck tension is akin to duct taping a spoiler on a rusted out Camry and thinking it gives you an edge so you can beat Sarge’s Challenger in the straightaway. LOL!
- April 3, 2016 at 10:49 pm #26775Doc HighwallParticipant
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I have been real busy getting ready for testing this summer. I have cast a lot of the SAECO #315 175 gr.TCGC match bullets with my 30:1 alloy. The bullets I am going to use weigh an average of 174.5 grains held +-.4 grains, or 174.1 grains to 174.9 grains for a .9 grain tolerance. I have over 800 of these, now I have to size and lube them in different sizes of .3100″ .3105″ and .3110″, I plan to start the test with a .3100″ bullet and a .3090″ expander.
I took my 300 Lapua Palma case with the small rifle pocket and de-primed, washed and annealed them. Today I weighed them and I have 284 of the that weigh an average of 170.85 grains and they weigh between 170.4 grains and 171.3 grains for a tolerance of .9 grains that I am going to use, 16 are out of that tolerance. The average wall thickness in the middle of the case necks averages .01445″ and I will use this measurement to determine which neck bushing I will use for the test
All the weighing has been done with a Acculab VIC-123.1 scale.
I will neck size them with my Redding competition die with the sliding chamber, and expand the case necks with my modified Forester bench rest seating die that I made into a case neck expander with a sliding chamber and floating expander. I want to do the case neck sizing X number of days before loading and shooting them so as to keep things the same for neck tension.
For lot control the bullets are from the same lot of alloy, along with gas checks, cases, primers, and powder.
I have to decide what bushing to use for test, with a average wall thickness of .01445″ and a .3100″ diameter bullet the loaded round neck diameter will be .3389″ ,with a .3105″ bullet will be .3394″ and with a .3110″ bullet will be .3399″ . I don’t want the difference in the neck sizing bushing vs. expander diameter make a difference and skew the test results.
I have sizing dies for my bullets starting at .3080″ to .3110″ in .0005″ increments and I have floating expanders to also match in .0005″ increments. This way when I start with a .3100″ and a .3090″ expander, and then use a .3105″ I will be able to use a .3095″ expander maintaining a .001″ neck tension.
- April 11, 2016 at 1:23 pm #26919dvernaParticipant
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I assume you already have a history of how the gun shoots with the same protocols of bullet culling, case prep, and sizing but without annealed cases? I am curious if those results show groups that exhibit a greater degree of vertical stringing than horizontal dispersion.
Really looking forward to your test results. There is a lot of effort going into this!!
Thank you for sharing with us
- April 11, 2016 at 5:21 pm #26928popperParticipant
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As long as we are musing, whatever it is should be consistent! I FL size after annealing. Some say the neck should be sparkling clean inside, others want that carbon film to aid in neck tension. I can’t tell the difference. Doc’s test results will be interesting but IMHO specific results will only apply to his alloy/load/etc. There may be some general ‘rule’ to apply.
- April 11, 2016 at 8:29 pm #26932Doc HighwallParticipant
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Popper, in my tests the necks will be annealed each time before sizing as a control. I will start the test with a .3100″ bullet cast of 30:1 alloy and use a .3090″ expander. The optimum powder charge after it is found will be used as a starting point for progressing up in bullet diameter and expander diameter, maintaining a consistent .001″ neck tension. After the optimum bullet diameter is found using only .001″ neck tension, then I will play with varying the neck tension in .0005″ increments. These tests are designed to show that neck tension does make a difference, and as a final test one control group will be continued to be annealed and shot, and the second group will start out being annealed and only be reloaded and shot there after. This will show just how fast cases get work hardened in just a few loading’s, and how the accuracy is affected.
I am taking great pains to ensure that all components are from the same lot, and nothing is taken for chance.
I will brush the insides of the necks before annealing and make sure they are clean enough that it does not affect the annealing process. What I don’t want is for a case to have excess bullet lubricant on the case neck, that when the induction annealing starts that the is no dissipation of heat carried away by bullet lubricant evaporating.
Worst case scenario I will give the cases a quick dry tumble to ensure they are clean, then anneal.
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