BS-Neck tension

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  • Last Post 24 August 2018
joeb33050 posted this 11 August 2018

 

Neck tension

 

There’s a test in TFS on this, John A. knows where. Neck tension affecting accuracy with < ~.75” groups may happen, but if so, the test results are well hidden.

 

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Geargnasher posted this 12 August 2018

What matters most is CONSISTENT BULLET PULL, and it matters a great deal. I can create flyers 2 or 3 inches outside of the group, on demand, with rifle calibers feom .22 to .30, simply by throwing in a cartridge that required noticeably less effort to seat the bullet.

That said, the inconsistency is relative to POI, not necessarily to group size. Sorted by seating effort, it is possible to shoot several equal, or nearly equal, groups with different points of impact.

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joeb33050 posted this 12 August 2018

What matters most is CONSISTENT BULLET PULL, and it matters a great deal. I can create flyers 2 or 3 inches outside of the group, on demand, with rifle calibers feom .22 to .30, simply by throwing in a cartridge that required noticeably less effort to seat the bullet. That said, the inconsistency is relative to POI, not necessarily to group size. Sorted by seating effort, it is possible to shoot several equal, or nearly equal, groups with different points of impact.
YOU DIDN'T READ THE ARTICLE. WRITE ONE, YOU SEEM TO HAVE A LOTTA OPINIONS. ANY Data?

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Geargnasher posted this 12 August 2018

I don't have access to the article, and am responding to your BS topic in general with the conclusions of 25 years of my data. Anyone can easily duplicate it.

If you don't believe me, prove it wrong, with your own tests.

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John Alexander posted this 13 August 2018

"What matters most is CONSISTENT BULLET PULL, and it matters a great deal. I can create flyers 2 or 3 inches outside of the group, on demand, with rifle calibers feom .22 to .30, simply by throwing in a cartridge that required noticeably less effort to seat the bullet."

Geargnasher

With all due respect, I think you are going to have a very hard time showing that consistent bullet pull "matters a great deal" much less "matters most".  In fact, think it is going to be hard to show that it matters at all.

I could say that in my 40+ years of experimenting with cast bullets I have never been able to show that consistent bullet pull matters one whit in the type of rifles used in CBA competition.  But that shouldn't carry any more weight than your statement that it causes huge fliers. Neither amounts to much more than anecdotal evidence without a well run experiment to back it up.

Fortunately, I don't have to do that because Gerry Bottiiger has already done it with an elaborate well designed set of experiments that showed that neck tensions that vary by near 100% had no effect of either accuracy or muzzle velocity.  In effect accepting the challenge in your post above 5 years before you made it. Gerry's article was published in TFS #223 and 224 in 2003, and no one has refuted his finding in the intervening years. His two articles can be found in the CD for Fouling Shots from 2008 - 2015 for sale at our website for $14.95. One of the advantages of being a CBA member is being able to read such articles when they are published.

If you would PM me your email address I would be happy to send you a copy of a later Fouling Shot article in which I reviewed Gerry's work and expanded on the subject -- at no cost.

John

 

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Ken Campbell Iowa posted this 14 August 2018

my obsessive mj benchrest buddies assure me that the brass neck expands before the bullet moves much ... and so i have this mental image of ....

at the shot the tight or loose neck tension doesn't count anymore... and the bullet is just left there, in mid-air ... free to flop or twist however the gases push it .... 

so maybe we should make the turned neck a very tight fit in the chamber :::   same od as the chamber neck id ... the case neck at firing does guide the bullet .... almost like a breech-seated bullet ........ ( dangerous? ... probably not with lead bullets and loads worked up with this arrangement in mind . )

***************

the above is a recurring mental image i harbor .... not sure if it has merit ... but after i get some other projects done i am betting a match barrel and about 3 days of shop time on it.  probably 6mm ....  what could go worng ?

ken  

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pat i. posted this 14 August 2018

I think Dave Lee and maybe a few other guys out west did or do use an interference fit like you're describing. I could be wrong but don't think so and if they did/do you can't deny the results.

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John Alexander posted this 14 August 2018

Bob Birmley's fairly recent articles on "Going for Records or some such title talks of this method. One part of the article that I don't disagree with.  And Pat is right. Dave Lee and his disciples were hard to beat and still hold records.

John

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Larry Gibson posted this 15 August 2018

I prefer to use .002 - .003 neck tension simply because it holds the GC'd bullets securely in the case neck. I've not found that neck tension alone can be attributed to accuracy enhancement.  I have found that too much neck tension can cause damage to the bullet during seating, especially PB'd cast bullets of softer alloy, during seating by swaging the bullet down and causing damage to the nose from the seating stem.  Also too much neck tension with GC'd bullets can cause excessive run out as the GC expands the case neck.

Sizing to minimal .002 - .003 tension also reduces the working of the case necks giving longer case life and more firings before annealing may become necessary.  I used bushing or collet dies and proper size expanders in M dies to achieve that amount of neck tension.

LMG  

Concealment is not cover.........

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John Alexander posted this 15 August 2018

Larry is right, of course, there are all kinds of ways that the WRONG NECK TENSION can cause all kinds of problems both to little and too much neck tension.

Gearnasher's statement was that shot to shot VARIATION in neck tension was very important. Bottiger's research with a combination averaging very close to .5 MOA has blown that claim out of the water.

The most interesting thing about variation in neck tension is that people continue to think it is important in spite of it being debunked as completely as it could possibly be. No wonder we haven't progressed in this century.

John

 

 

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Ken Campbell Iowa posted this 15 August 2018

... i find it interesting that in mj benchrest ... some midwest top shooters are working with a cartridge ... that has almost no neck at all ...... and are doing very well with it ...  this might be worth a go in cast shooting ...  the idea is that the case is located by pushing the tapered shoulder against the tapered front chamber  ... and then we can get creative with the freebore and throat..... mainly make it very snug .....

kinda like the often botched effort to push a tapered bullet against a tapered throat.  while better than a straight throat in theory .... there really isn't a lot of rifling to taper .... 1 degree per side only grabs about a quarter inch of the bullet ...

i need one of those " limitless " brain pills to consider the ramifications of a neckless case ...  but worth a mild migrain i spose ...

ken

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pat i. posted this 15 August 2018

I wonder if after a couple of thousandths adding more tension does anything at all. The bullet acts as an expander so everything after what's required to grip it might be wasted effort.

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OU812 posted this 16 August 2018

more neck tension will help chamber a snug fitting bore riding bullet. not enough tension could cause bullet to slip back into case and not chamber deep enough.

I wonder what type of cast bullet Bottiger was using during his test...bore rider, taper bumped bore rider, taper bumped loverin...?

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joeb33050 posted this 16 August 2018

I don't see any change in mv or accuracy with varying neck tension; and I don't understand why neck tension is measured in thousandths of an inch. If a set of cases is neck sized and then pushed in/out of an M die, there is a wide variation in force required to get the neck on and off the spud. Diameter AND hardness of the neck combine to determine the force required at the M die. This with necks brushe3d.  Neck turning and annealing may reduce the variation. I have had instances of seating a long bullet where the seating bumped up the shoulder/body area, changing bolt closing force.

 

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RicinYakima posted this 16 August 2018

"I don't understand why neck tension is measured in thousandths of an inch. "

Very few of us have a way to measure the force required to push the bullet into the case neck, I've never seen such a scale in the home reloading shop. But we all have micrometers to conveniently measure before and after seating neck diameter. I know it is not a very good accurate way to do it, but it is fast and easy.

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John Alexander posted this 16 August 2018

 

 

 

Pat asks:
"I wonder if after a couple of thousandths adding more tension does anything at all. The bullet acts as an expander so everything after what's required to grip it might be wasted effort."
========

Mike Barrett has done experiments to find out and he found just what you expected beyond a point sizing smaller to get more tension does nothing at all. The bullet simply expands the case neck as it is seated. 

According to Mike (a rare CB shooter who tries to find answers instead of taking somebody's word for it) claims it is wasted effort.

John

 

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John Alexander posted this 16 August 2018

OU812 sez:

more neck tension will help chamber a snug fitting bore riding bullet. not enough tension could cause bullet to slip back into case and not chamber deep enough.

 

I wonder what type of cast bullet Bottiger was using during his test...bore rider, taper bumped bore rider, taper bumped loverin...?

=======

You are right too much neck tension or too little can cause a multitude of problems. I discussed them at length in my article in TFS #240. On the other hand, shot to shot VARIATION in neck tension, which Bottiger investigated has NO EFFECT on either accuracy or muzzle velocity. Why we continue to get our knickers in a twist about this instead of worrying about some factor that may be real is a mystery to me. 

I believe Bottiger was using the Ardito approach with bumpted Eagan MX4ARD bullets but I haven't read his article recently

Anybody serious about this topic should go back and reread Bottiger's article if for nothing else as how an experiment should be run.

By the way Bottiger used a device to measure the actual force to seat bullets not just the ID neck diameter.

John

 

 

 

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Ed Harris posted this 18 August 2018

In fixed ammo for magazine feed I want the expander plug 0.002" less than bullet diameter so the bullet has a snug fit.

Greater interference than that will deform soft bullets.

Less tension might cause bullets to telescope during feed cycle.

But in boltguns which are single-loaded I seat bullets to hard contact with throat and origin of rifling and neck tension does not affect shot-start pressure.

Larry, John and Joe all have valid points.  Depends upon the circumstances.

But I don't care to shoot competition anymore. I tinker with my own rifles to get the results that I want.

I have learned a few things over the years, and will share, but feel free to ignore me, I really don't care.

 

73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia

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Paul Pollard posted this 20 August 2018

In January, 2013, I did a test trying to hold the bullet at a consistent OAL. Previous testing had shown that an OAL of 2.210" was the best place to seat for accuracy. This is the 6ppc with the Eagan MX2-243 bullet. As can be seen from the chart, the loosest bushing at 0.261 was enough to hold the OAL at 2.210. The start length and end length were checked on chambering and as tension increased, the bullet could be held at a longer length. This test was not a test for accuracy at different tension, but to find where the bullet quit moving deeper. I could probably use the 261 bushing, but decided on the 259 Nitride bushing. Note the differences in neck diameters with dies marked the same. I also found that trying to jam the bullet deeper into the rifling was counter productive.

 

Bushing Chart and Neck Tension

 

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Geargnasher posted this 20 August 2018

Larry is right, of course, there are all kinds of ways that the WRONG NECK TENSION can cause all kinds of problems both to little and too much neck tension.

Gearnasher's statement was that shot to shot VARIATION in neck tension was very important. Bottiger's research with a combination averaging very close to .5 MOA has blown that claim out of the water.

The most interesting thing about variation in neck tension is that people continue to think it is important in spite of it being debunked as completely as it could possibly be. No wonder we haven't progressed in this century.

John

No, John, the reason why you haven't progressed in this century is because of myopia, group think, and lack of curiosity.

You and others have gone far out of your way to prove my statement "wrong", and not a single one of you ever stopped to ask, "What is it that Geargnasher is doing differently that would cause the uniformity of neck tension to matter in his shooting, and why would he choose a loading technique that introduces that variable?"

I'm tired of your resistance to learning, so have fun doing it the same old way and I'll get back to more productive endeavors.

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pat i. posted this 20 August 2018

Anyway....Paul I expect the bullet to seat deeper into the rifling when using a tighter button but wonder if once the bullet was seated and the case expanded if it would take any more force to get it moving no matter what size button you used. My gut tells me it wouldn't. Could be wrong though.

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