Effect of neck tension on accuracy

L

londonhunter

Guest
Hi to all
I Best describe myself as a hunter who aspires one day to be a bench shooter

I reload and shoot the following calibers on a regular basis
I have been lurking around for some time and appreciate some input from bench shooter their opinion on neck tension and accuracy
I have always been instructed by my peers to buy bushing so the net neck tension is 0.001 over measured
I also understand you guys shoot mainly single shot manual feed and some of my guns are multiple shots hence high neck tension is needed
My question is how much and is accuracy the benchmark for selecting what tension one shoots at ?

After load development I now ended up with varying tension from 2 thousand to 4 thou
Sand
My main calibers are
20 tactical
6x47lapua
6mmppc
6.5x55 sewed
Thanks In advance
 
My question is how much and is accuracy the benchmark for selecting what tension one shoots at ?
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It is not the benchmark. The benchmark is the target.

Having said that, you need to understand that there are a number of aspects of reloading that are purely empirical. Any *right* answer involves testing with the particular components used. Change one of the settings and you might need to change another.

There are a lot of people who don't do their own testing, or don't do all their own testing. They say "Oh, famous shooter so and so does this, that has to be the way to go." Benchrest falls prey to fashion just like any other sport.

Making decisions harder, this is a matter of degree; to some extent, we all work off the successes of others, and that too is a good procedure.

Generalities out of the way, here is an example: Back in the early 1990s, a typical powder used with the 6PPC was 322. Neck tension, with a Wilson seater, was light -- thumb pressure, sometimes less -- "finger pressure." As the manufacture of 322 changed, and people discovered N133, neck tension went up significantly. Press required.

Example out of the way, What we (well I) believe is neck tension is one part of the equation that sets the slope of the ignition (pressure) curve. Bullet seating is another, as is primer, powder, i.e., all the elements.

There is no "ideal" pressure curve. Different rifles (barrels) will shoot better with one opposed to others. There is as yet no science to predict what works best. There is not even a model that predicts "Oh, you can ignore *that* one. Sometimes you can. You are left with testing. Change a component, retest. And sometimes testing shows no difference. Let that happen to you a couple of times and you conclude "Oh, that doesn't matter." But sometimes it does, and you'll miss it, and throw away a perfectly good barrel because it doesn't behave the way you think it should. Well, $hit happens.

EDIT: Remember too that all this about the pressure curve is what I and some others believe. It is a grasp at beginning to model the process. It could also be quite wrong. We just don't know for sure.

Finally, remember that in benchrest, both the size of the group and especially the consistency of of the groups ("agging") are what determines winning, which is the goal. The aggregate size that wins over what comes in second -- or tenth, for that matter -- is quite small. Essentially, it is insignificant for anything other than benchrest shooting -- usually .050 inches.

The goal in hunting, varmint or otherwise, is quite different. There are points of crossover obviously. But as with any two sports, there is also a danger of saying "Oh, I know XYZ, I've already proved it."
 
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Are you using bushing dies? Are you shooting over flags? The reason that I ask these questions is that you will need the former to test different neck tensions, and the latter to be able to do any proper accuracy evaluation.
 
On Neck tension:

Last year about this time I visited a friend way out of State and was shooting with him. I asked him what his seating depth was and he said he thought he may be jumping about .050", if I recall correctly. He went on to say that he was using "fitted necks". I assumed that to mean he was using brass with necks turned to exactly fir the neck of the chamber when loaded, WRONG!

The fitted necks are made so that a big doughnut forms on the inside of the case neck and the neck turned with clearance so that the necks have almost no neck tension. The bullets just sit on the doughnut. I had heard of folks shooting cases with necks slit, etc but this was a first for me.

Conclusion here: Neck Tension is only important if one is using it to keep bullets at a sepcific seating depth to affect tune. I suppose a case could be made that varying neck tension can affect tune for folks jumping their bullets but I think, for the most part, it only matters to hold bullets fast in a speciffic position and those who believe it to affect tune are jamming heir bullets into the lands. Perhaps I am wrong about this but I haven't experienced anything different than what I stated here. Neck Tension's importance may be one of the 69 Benchrest Myths.

Obviously for anything but Benchrest activities one can't easily use "Fitted Necks".
 
Pete,
A long time back, a fellow that shoots with a current world record holder, and at any given match is competitive with him, told me that they found that 133 "likes" a lot of neck tension (.003). I tried this, with the same load and seating depth (in the rifling, not jumping), and my groups improved. Later, experiments showed that there are powders that "don't care" about neck tension. This was the case with an old lot of 2015.

londonhunter:
Test.
 
Boyd Allen said:
Pete,
A long time back, a fellow that shoots with a current world record holder, and at any given match is competitive with him, told me that they found that 133 "likes" a lot of neck tension (.003). I tried this, with the same load and seating depth (in the rifling, not jumping), and my groups improved. Later, experiments showed that there are powders that "don't care" about neck tension. This was the case with an old lot of 2015.

londonhunter:
Test.
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Boyd, I believe it's all about building pressure. When I begin tuning I find the spot where the particular bullets I am using just kiss the lands using .002 neck tension and closing the bolt on the dummy round (30 Cal stuff). I then push the bullet back using my Forster Ultra seaters, which show, in thousants, how many thousants is required until I can just barely see land marks.( I also check the OAL with a Stoney Point Comparitor on my Vernier Caliper) That is generally .012. I don't know about smaller caliber bullets but I would assume they are basically the same. If I go to .004 neck tension and do the same thing, it takes .015 or so to get to the same place where I can just see faint land marks. So, one can concluse that by going up .002 in neck tension one has allowed their bullets to seat .003 deeper into the lands, which increases pressure, eh? .003 will take a rifle out of tune almost every time, from my experience iover the years.
 
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About tuning Generally:

Years ago when I was just getting started in Centerfire Benchrest I was on here asking questions about tuning. Back then a young fellow who called himself Dr D, who contributed here, sent me a long private message outlining how his father had taught him to tune, using seating depth as the basis for making rifles shoot. I have followed his formula since and have not had it fail me as yet. His method pretty much cuts through the "Black Magic".
 
Pete,
I think that in the case of short range bullets in a 6PPC with 133, that the powder likes a particular pressure profile as the bullet is engraving. This is distinct from the peak pressure that happens a little farther down the barrel, so simply increasing charge may not do the same thing. With different powders, calibers, and bullets I would have to test. What caliber, bullets and powder to you use the most?
 
I would love to see pressure traces of light neck tension and then strong neck
tension in comparison. Seeing this with different powders would be interesting
 
You need to see some of my Red Cornelison BR brass. He rebated the rim to 223 size, Shortened the case and turned the OD of the neck approx .250 down from the case mouth. When he sized the brass it sized the bottom of the neck. It allowed him to set the bullet on the step in the neck. Way to labor intensive for me.
Butch
 
Pete Wass said:
Years ago when I was just getting started in Centerfire Benchrest I was on here asking questions about tuning. Back then a young fellow who called himself Dr D, who contributed here, sent me a long private message outlining how his father had taught him to tune, using seating depth as the basis for making rifles shoot. I have followed his formula since and have not had it fail me as yet. His method pretty much cuts through the "Black Magic".
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Pete;
Would you be so kind as to share that Tuning procedure with us????
You certainly got my attention!!
CLP
 
Bob Kingsbury said:
I would love to see pressure traces of light neck tension and then strong neck
tension in comparison. Seeing this with different powders would be interesting
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Bob, Ive done just that, and could see zero or very close to it, change in innitial pressures when jumping but you can see a slight change in pressures when jamming more or less, but I don't remember the exact numbers off the top of my head.--Mike Ezell
 
There is a description of "stepped necks" In Glenn Newick's The Ultimate in Rifle Accuracy, page 132. If you really have to have it all typed out, It'll have to wait until after the ball game, and until the whim strikes . . .

Edit: That's BSAEBALL game
 
Dr D's process:

Dr D sent me the private message because, at the time, anyone who offered anything different on BRC was FLAMED and ridiculed for not conforming to the 69 Benchrest Myths. ( Hasn't changed a great deal but some)

It has been a long time but I will do the best I can. I just turned 66 and have drank a lot of good likker over the years so my memory ain't the best.

Dr D, told me that when he tested loads he took a big box of loaded cases to the range with him segregated by powder charge and seating depth. He would find a load/bullet combination that worked and try to improve on it by first starting with bullets just touching the lands and increasing into the lands by .003 increments until he found the smallest group in that sequence. If the group looked like it could be smaller he would take the best seating depth and incerase the load by .2g to see if he could improve the group and decrease the load by .02 for the same reason and shoot them.

He weighed all the loads, as I recall; why I have weighed since. It has never made any sense to me to read where people JAM and go up x number of clicks. When one considers the built in error in measures and the unknown of how many thou one is either in or out because they have not measured their bullets for ogive length, they have left one helluva lot on the table. Sure, some of the best shooters seem to operate this way but they depend on averaging and not winning each and every match they shoot. Imagine how well they would do if they truly worked on making evey round be as exact as they could make it.

Bullets are a huge part of this equation. I have only measured one lot of 100 bullets, of all the thousands of bullets I have measured, in which every one measured exactly the same (ogive length). All the rest have had varying differences in measurment. It is very tedious work to try to load consistent OAL length loads, measured at where the bullet iwill touch the lands unless one segregates their bullets by the length of the ogive. It can be done but it takes HOURS to do.

A lot of emphasis is placed on Brass but if one anneals their brass to maintain constant neck tensioning ability, brass is never an issue. It's what goes in the brass that is the real issue and how one presents it all to the lands. Of course, all the sizing paramaters of Brass have to be correct and consistent; should go without saying.

In order to have consistent round groups, every bullet must be presented to the lands exactly the same. Loading randomly out of a box of bullets will never insure one presents their load as preciscely to the lands as they can. If one is playing the averages, it all obviously has worked and worked well for some but most of us are not that good and/or not that lucky.

Oh yes, there is the occasional barrel that will seem to shoot anything one throws in it. Unless one is willing to spend half their retirement nest egg on barrels, one won't see many or any of those barrels, from my experience, at least. In leu of spending the Egg Money, one can make their loads as perfect as they can be made and hope the averages swing their way, more often than not.

Years ago, the publisher of Car and Driver Magazine said in an editorial " If one looks out the window and everyone is running down the street in the same direction, it's probably not a coincidence". Now, take the RBS Chargemaster, for instance - - - - . Measure your bullets people and do what Dr D said. You will see improvement.
 
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Well I found I could cut my group sizes drastically by first rotating each case 180 degrees on second firing and neck sizing only. I size only 2/3 the length of the neck.

This centers the case and neck as near perfect as possible, and reduces the ammount of contact between case neck and bullet.

The less neck tension/pull strength the less variations in pull strength can affect the individual shot.

When I follow this method one holers are consistent.
 
Trying to hide in the back depths of this thread. A ton of excellent info here for the shooter-loader who is trying to learn and improve. Thank Gawd I haven't read and subscribed to the 69 myths.....

Can I post a pic in here of some groups I just shot and solicit comment on possible areas of improvement that may be evident and that may be load dependent ?
 
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