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chambered221 Super Member
Joined: Aug 17, 2007 Posts: 3455 Location: Lost for good !!!
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chambered221 Super Member
Joined: Aug 17, 2007 Posts: 3455 Location: Lost for good !!!
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Posted: Sun Jan 13, 2013 10:36 am Post subject: Re: Neck Tension |
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Seriously now ......... I've read some articles about neck tension in the past that only reinforced the too many variables concept.
Some shoot better with press fit bullets, others prefer a looser fit.
The thing that has always confused me is the press fit. No matter how much you shrink the neck it is always opened back up to the bullet diameter. Yet... the amount of under sizing can/will make a difference.
_________________ Ask as many people needed, sooner or later your question will be answered the way you want it answered !!!
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slimjim Super Member
Joined: May 16, 2009 Posts: 8314 Location: Fort Worth TX
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Posted: Sun Jan 13, 2013 11:05 am Post subject: Re: Neck Tension |
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Vince wrote: |
Be interested to see pics of the force scale mate, and how you set it up. I have always relied upon the standard neck sizer that comes with the dies.
I wonder what sort of difference there may be in velocity and POI on the target? Also, what effect this had on accuracy, if any. |
Thanks for the interest, Vince.
Here is how I set-up to measure the force required to extract a seated bullet. Now that I see the picture, the scale is working off a lever so the force measured is not the force of extraction (neck tension) which should be higher.
This test is not dependent on what type of die a reloader uses. It only measures the force of extraction between a new and fired case which has been sized to the same neck dimension. If I size the necks smaller, this force will go up (noticeably for the fired brass). If I size the necks larger, the force will go down. At the current neck size (.302 bushing for a .270), I'm going slightly beyond the 50 pound limit of this scale.
I could do some testing just for fun to see what the affect is on group size and point of impact. From my experience, I believe it will be measurable but I'm sure its significance is at longer ranges. For now, I use fired, resized brass when the POI is important, e.g., hunting with shot opportunities beyond 100 yards.
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_________________ "To anger a conservative, lie to him. To anger a liberal, tell him the truth." - Theodore Roosevelt
"The world is a dangerous place to live; not because of the people who are evil, but because of the people who don't do anything about it." - Albert Einstein
Last edited by slimjim on Sun Jan 13, 2013 11:28 am; edited 1 time in total |
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slimjim Super Member
Joined: May 16, 2009 Posts: 8314 Location: Fort Worth TX
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Posted: Sun Jan 13, 2013 11:12 am Post subject: Re: Neck Tension |
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chambered221 wrote: |
No matter how much you shrink the neck it is always opened back up to the bullet diameter. Yet... the amount of under sizing can/will make a difference. |
There is some elasticity in the brass so that when the bullet is pulled, the neck diameter of the case contracts. After I pulled these bullets, I could not insert them back into the cases by hand. I still had to press them back in.
_________________ "To anger a conservative, lie to him. To anger a liberal, tell him the truth." - Theodore Roosevelt
"The world is a dangerous place to live; not because of the people who are evil, but because of the people who don't do anything about it." - Albert Einstein |
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Elvis Super Member
Joined: Jul 27, 2008 Posts: 9239 Location: south island New Zealand
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Posted: Mon Jan 14, 2013 12:57 am Post subject: Re: Neck Tension |
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very nice set up thankyou for sharing that slim.
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Vince Site Admin
Joined: May 25, 2005 Posts: 15701 Location: Brisbane AUSTRALIA
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slimjim Super Member
Joined: May 16, 2009 Posts: 8314 Location: Fort Worth TX
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Posted: Mon Jan 14, 2013 7:46 am Post subject: Re: Neck Tension |
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I could run a test with every component the same except new brass vs fired brass and measure the difference in POI and accuracy. It will give me something to do this summer.
_________________ "To anger a conservative, lie to him. To anger a liberal, tell him the truth." - Theodore Roosevelt
"The world is a dangerous place to live; not because of the people who are evil, but because of the people who don't do anything about it." - Albert Einstein |
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slimjim Super Member
Joined: May 16, 2009 Posts: 8314 Location: Fort Worth TX
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Posted: Sat Apr 13, 2013 7:34 pm Post subject: Re: Neck Tension |
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Well, I've tried several attempts to measure the effects of crimping on neck tension. I went out and got myself some Lee crimp dies. Using the crimp feature built into my Redding bullet seating dies is too finicky. If everything isn't perfect the crimps are inconsistent and I found could bulge the neck. The Lee crimping dies do not require a consistent case length to function. I did some tests with my six8 and .270 Win with the Lee equipment. I used 150gr Berger VLDs in both brass cases. The Lee crimping die is a collet that presses inward on the case and has enough leverage to deform the bullet with the crimp. I can't say I have learned anything definitive but I thought that I’d share what I have found and see what comments you might have. I used fired brass that was sized and ultrasonically cleaned so did not have any powder on the inside of the neck. The longer necks on the .270 did result in higher neck tension than the shorter neck of the six8. Note, there is a mechanical advantage with the press so the true force to extract is higher than what I recorded.
The average extraction force of the 8 bullets from the six8 was 9 pounds without a crimp (4) and 11.1 pounds with the crimp (4). Force was about 20% higher with the crimp but variation in force did not get signnificantly better with the crimp.
The force to extract the bullets from the .270 was higher but my first attempt caused nothing but confusion. I loaded 4 and crimped 2 of them with a heavy crimp. Force varied from 24 to 44 pounds with no correlation to the crimp. The crimp was strong enough to deform the bullet and leave a groove where the crimp occurred. So I loaded up 10 more and crimped 5 with a light crimp. The ones without a crimp averaged 32 pounds (22 to 43 lbs). The ones with a light crimp averaged 25.5 pounds (21 to 32). It made me think that the crimp may have been bulging out the neck below the crimp causing a reduction in overall neck tension. So I loaded and crimped 4 more with a heavier crimp. I got nice consistency out of the first three, 34 to 36 pounds, then the fourth one slipped out with only 12 pounds of force (lowest ever for the .270 and it had a crimp?). I’m not eager to run more cases through this drill without figuring out what is happening. Going forward, I will continue to crimp the six8 just because I did get a slightly higher force and that can’t hurt with an autoloader. For my bolt action .270 , I’m not going to crimp when I’m using grooved bullets like the Barnes TTSX and Hornady GMX. The grooves in these all-copper bullets do increase neck tension as the neck grips the grooves. The lead-core VLDs have been very consistent shooters without the crimp (1/2 MOA). I may continue working with the crimp on the legacy lead-core bullets just to learn more. Eager to hear your thoughts.
_________________ "To anger a conservative, lie to him. To anger a liberal, tell him the truth." - Theodore Roosevelt
"The world is a dangerous place to live; not because of the people who are evil, but because of the people who don't do anything about it." - Albert Einstein |
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Pumpkinslinger Super Member
Joined: Sep 22, 2007 Posts: 5001 Location: NC foothills
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Posted: Sun Apr 14, 2013 1:51 pm Post subject: Re: Neck Tension |
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The last time my neck crimped the chiropractor was able to fix me right up!
Sorry about that.
Slim, good effort and info there!
_________________ Mike
"I ain't no better than anybody else, and there ain't nobody better than me!" Ma Kettle |
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gelandangan Super Member
Joined: May 07, 2006 Posts: 6396 Location: Sydney Australia
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Posted: Sun Apr 14, 2013 2:41 pm Post subject: Re: Neck Tension |
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+1, but I go to physio..
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slimjim Super Member
Joined: May 16, 2009 Posts: 8314 Location: Fort Worth TX
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Posted: Sun Apr 14, 2013 2:58 pm Post subject: Re: Neck Tension |
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Maybe I should visit a witch doctor. I was expecting more consistency in the results. It was disappointing that there wasn't a direct correlation to increased and more consistent neck tension when crimped.
_________________ "To anger a conservative, lie to him. To anger a liberal, tell him the truth." - Theodore Roosevelt
"The world is a dangerous place to live; not because of the people who are evil, but because of the people who don't do anything about it." - Albert Einstein |
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gelandangan Super Member
Joined: May 07, 2006 Posts: 6396 Location: Sydney Australia
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Posted: Sun Apr 14, 2013 3:43 pm Post subject: Re: Neck Tension |
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Slim, the pressure exerted by the neck could be considered as minor as compared to the pressure subjected tot he whole system when the powders are combusted.
Although uniform neck grip does increase in the uniformity of the end velocity, it is but one of many elements that contributed to the cause.
In fact, in the old days when boolits are paper patched, the whole neck tension is the result of the fit of the paper to shim the gap between the neck and the boolit.
Yet there are historical records of amazing shots with them.
_________________ A straight line is the shortest distance between two points.
A smile is the shortest distance between two people.
Do - Not try!
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slimjim Super Member
Joined: May 16, 2009 Posts: 8314 Location: Fort Worth TX
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Posted: Sat Apr 20, 2013 2:34 pm Post subject: Re: Neck Tension |
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Was at the work bench fiddling around so took four .270 cases, sized them, seated bullets, crimped them, and pulled them. Average extraction force was 32.3 pounds with a std dev of 5. Then for grins and without touching the necks, I reloaded all four cases, did not crimp them, and pulled them again. I wanted to see how much the neck tension would be reduced after a bullet had been through the neck once. Do you want to take a guess what the average neck tension was? Come on guess.
32.1 pounds but the std deviation doubled to 10.
_________________ "To anger a conservative, lie to him. To anger a liberal, tell him the truth." - Theodore Roosevelt
"The world is a dangerous place to live; not because of the people who are evil, but because of the people who don't do anything about it." - Albert Einstein |
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slimjim Super Member
Joined: May 16, 2009 Posts: 8314 Location: Fort Worth TX
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Posted: Sat Apr 20, 2013 2:47 pm Post subject: Re: Neck Tension |
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All right, why not do this one more time. Seat bullets back into the untouched cases but crimp them this time. Results.
Extraction force dropped a little bit down to 29.1 (3rd time a bullet had been seated into the neck) but the std dev dropped back down to 6.
So far it looks like the .270 has about 3 times more neck tension than the 6.8 most likely due to the longer case neck and I use a 0.002" tighter neck bushing when I resize the case. It also appears the the std deviation is improved with the crimp but on the .270 it has enough neck tension that it doesn't really increase neck tension. Again these are with lead-core bullets. I would not crimp an all-copper bullet like Barnes.
_________________ "To anger a conservative, lie to him. To anger a liberal, tell him the truth." - Theodore Roosevelt
"The world is a dangerous place to live; not because of the people who are evil, but because of the people who don't do anything about it." - Albert Einstein |
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MacD Super Member
Joined: Apr 08, 2011 Posts: 1052 Location: Canada
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Posted: Sat Apr 20, 2013 3:57 pm Post subject: Re: Neck Tension |
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The variables that relate to brass are both within and outside of our control. The alloy itself will in part determine elasticity and resistance to work hardening. The annealing at the factory between the steps necessary to produce the finished case plays a part. The relative thickness of the case wall will affect neck tension. Finally the diameter of the bullets also may vary slightly. We live in an anolog world which we measure digitally. Thank the maker for variabilty. It makes it all interesting doesn't it.?
Try the same bullets in the same cases and see if extraction force decreases consistently. I am betting it won't.
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