neck tension
- Thread starter sako2
- Start date
Nathan,
The usual formula is 3 times SD = ES, not 6. It is approximately true for a sample size of 10 rounds, where your set of data are average. For other sample sizes the multiplier is as shown for up to 50 in this table, but once you get above a sample size of about 7, the standard formula for SD is better than the multiplier just because a larger number of shots starts to give outliers too many chances to appear.
The usual formula is 3 times SD = ES, not 6. It is approximately true for a sample size of 10 rounds, where your set of data are average. For other sample sizes the multiplier is as shown for up to 50 in this table, but once you get above a sample size of about 7, the standard formula for SD is better than the multiplier just because a larger number of shots starts to give outliers too many chances to appear.
As i mentioned in 1 of my other threads i was getting a bolt swipe on my brass. So i never made it to the max charge. Apparently the rim on Adg brass is thicker. Yesterday i loaded some hornady brass up to the max charge and i have no bolt swipe, bolt opens easily. And my es came down to 20 fps. Kilo is right Magpro wants to be compressed. Thanks everyone for your help.
Case "neck tension" is typically expressed in thousandths of an inch.
It takes much more force to push a 30 caliber bullet out of a case with .020 inch neck wall thickness than one with .010 inch" neck wall thickness and both have .001 inch "neck tension."
There's sound reasoning behind the force needed to push or pull bullets out of case necks being the industry standard. It's called bullet pull force.
It takes much more force to push a 30 caliber bullet out of a case with .020 inch neck wall thickness than one with .010 inch" neck wall thickness and both have .001 inch "neck tension."
There's sound reasoning behind the force needed to push or pull bullets out of case necks being the industry standard. It's called bullet pull force.
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My "guess" is that neck tension is determined by the resized case neck with a certain case thickness as mentioned above in relation to the bullet diameter. One remedy is to take a mandrel and size the inside diameter to a consistent width and turn off the excess so neck thickness is consistent so the future outside neck resizing of the brass is consistent. Another method might be to take a neck sizing mandrel used by cast bullet makers and enlarge the inside diameter of the case neck so your resistance will be the same. The only caveat would be that the thicker necks still might provide more resistance because of the extra metal but I think this is minimal.
I messed around using a load cell and a arbor press a couple of years back and made a few observations about surface friction and neck tension.
- When starting to seat a bullet "x" amount of pressure was needed to start the bullet moving into the case.
- Once initial surface friction was overcame pressure dropped but you could cause spikes by simply increasing the pressure on the arbor handle which simply cause th ebullet to enter the casing faster
- the same would apply to pulling bullets. Initial pressure to overcome surface friction and the harder the pull the faster the bullet would exit
- using lubes decreased the seating tensions and made the seating pressure required more consistent but had little or no effect on velocity consistency or on paper
to get a true measurement would require a electronic control to ensure that the pressure would be even otherwise any measurement is iffy at best. rather than run down a rabbit hole of guesses it's better to just go shoot and see what works on paper
Bryan Litz did a study where he found that what we normally call a "neck tension" of .003 - 004 provides the most consistent velocities. My own studies which were casual at best showed me that lubing the neck or bullet using dry and liquid lubes had no effect at all on velocities.
I found by having a consistent neck thickness and ensuring my cases were sized to give a firm hold on the bullet without damaging the jacket gave me the consistent grouping I was wanting. I use .004 neck tension on my BR rifle and at 100 yards I get .1 to .2 MOA and on my F class rifles less than .75 MOA verticals (20 round groups) out to 800 yards using .003 on both the .260 Rem and the 6 BR . I wish that pesky wind was as easy to beat as the reloading was.
- When starting to seat a bullet "x" amount of pressure was needed to start the bullet moving into the case.
- Once initial surface friction was overcame pressure dropped but you could cause spikes by simply increasing the pressure on the arbor handle which simply cause th ebullet to enter the casing faster
- the same would apply to pulling bullets. Initial pressure to overcome surface friction and the harder the pull the faster the bullet would exit
- using lubes decreased the seating tensions and made the seating pressure required more consistent but had little or no effect on velocity consistency or on paper
to get a true measurement would require a electronic control to ensure that the pressure would be even otherwise any measurement is iffy at best. rather than run down a rabbit hole of guesses it's better to just go shoot and see what works on paper
Bryan Litz did a study where he found that what we normally call a "neck tension" of .003 - 004 provides the most consistent velocities. My own studies which were casual at best showed me that lubing the neck or bullet using dry and liquid lubes had no effect at all on velocities.
I found by having a consistent neck thickness and ensuring my cases were sized to give a firm hold on the bullet without damaging the jacket gave me the consistent grouping I was wanting. I use .004 neck tension on my BR rifle and at 100 yards I get .1 to .2 MOA and on my F class rifles less than .75 MOA verticals (20 round groups) out to 800 yards using .003 on both the .260 Rem and the 6 BR . I wish that pesky wind was as easy to beat as the reloading was.
Without the case neck thickness and hardness as well as contact area on the bullet, a given interference fit dimension can have a wide range of force required to push bullets out.
3 to 4 thousandths seems several times as much. You'll need the die neck diameter to be 5 to 6 thousandths smaller than the cartridge neck diameter to do that. I think a lot of copper will be scraped off bullets doing this.
2 thousandths smaller die neck is typical these days. And gives about 1 thousandth interference fit.
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can you rephrase all of that? Bart, are you saying 3-4 thousands case neck thickness as the difference from the outside case neck diameter to the inside case neck diameter?
Would another approach be to seat and pull a bullet thus using the bullet as a mandrel. Then, take the inside diameter and turn the neck to a consistent thickness?
Would another approach be to seat and pull a bullet thus using the bullet as a mandrel. Then, take the inside diameter and turn the neck to a consistent thickness?
like I said Bart to me the proof is on the target, theorize to your hearts content but I am getting results on the targets so I must be doing something right. Funny thing is my reloading procedure is dead on simple and my tools are bargain basement with the exception of my sizing dies (Redding or Whidden bushing dies) which I consider the most important part of the process
the way I check my neck tension is simple and fool proof. Size a case , measure the OD of neck, seat a bullet, remeasure. That is my neck tension if there is less than .003 expansion on the second measurement I go down another .001 on the bushing until I get a minimum of .003 difference. Ever see a bullet that has been sent down a barrel ? That rifling gouges bullets a plenty. That is why I like to buy use blems. I don't sweat the small stuff. When I miss the ten ring 99% of the time it is me not judging wind or mirage right, not the bullet or rifle.
the way I check my neck tension is simple and fool proof. Size a case , measure the OD of neck, seat a bullet, remeasure. That is my neck tension if there is less than .003 expansion on the second measurement I go down another .001 on the bushing until I get a minimum of .003 difference. Ever see a bullet that has been sent down a barrel ? That rifling gouges bullets a plenty. That is why I like to buy use blems. I don't sweat the small stuff. When I miss the ten ring 99% of the time it is me not judging wind or mirage right, not the bullet or rifle.
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The problem is that everyone is actually describing interference fit with the neck, not tension. As Bart points out, if the brass is thicker, the pressure needed to stretch the brass the same amount is greater. That pressure, multiplied by the contact area between the bullet and neck and by the coefficient of friction between the two will give you bullet pull force.
Answer to both questions is No.
Interference fit is the difference between resized case neck inside diameter and the bullet's diameter.
Use a neck turning tool with a steel pilot mandrel to uniform neck wall thickness uniformly:
https://www.midwayusa.com/case-neck-turners-and-reamers/br?cid=10455
You may need to resize the case neck after uniforming its thickness.
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Wowzers! I would destroy billets with that kind of neck tension. At 0.003”, bullets had a firm ring in them. In my testing less was more generally and I think I arrived at 0.0015” approximately as perfect with graphite lube in the neck. Necks annealed. I need more testing to proclaim any value from these numbers, but they did work once for me.
@UncleNick - that's great but in the real world most of us do not have the training or equipment to determine real neck tension. For those who want to then clean the brass to bare metal, measure the thickness to .0001 and here is the math
https://study.com/academy/lesson/elasticity-of-materials-moduli-measurements.html
so instead I use the interference fit and call it neck tension, it uses tools that every reloader haas on the bench all my range buddies know what I am talking about when I use the term and I can judge the effects of changes with a target and a chronograph with the chrono being optional
@ Nathan
Litz, Bryan. Modern Advancements in Long Range Shooting Vol. 2: Volume II . Applied Ballistics, LLC.
in table 6.5 Litz calls .0005 interference as very light, .001 as light, .002 as nominal .003 as relatively heavy .004 as heavy and .005 as very heavy and likely at that point to damage bullets. In his tests he found .003 provided the most consistent velocities in .223 and .243 and with .308 it did not matter. I choose to use .003. With cases where some or all of the brass has been work hardened enough to display springback after sizing I go with .004 to allow for the springback so the brass ends up at what most shooters and myself call .003 to .004 neck tension. I chamfer the mouths, do not use any lube and never had any copper shave off yet.
https://study.com/academy/lesson/elasticity-of-materials-moduli-measurements.html
so instead I use the interference fit and call it neck tension, it uses tools that every reloader haas on the bench all my range buddies know what I am talking about when I use the term and I can judge the effects of changes with a target and a chronograph with the chrono being optional
@ Nathan
Litz, Bryan. Modern Advancements in Long Range Shooting Vol. 2: Volume II . Applied Ballistics, LLC.
in table 6.5 Litz calls .0005 interference as very light, .001 as light, .002 as nominal .003 as relatively heavy .004 as heavy and .005 as very heavy and likely at that point to damage bullets. In his tests he found .003 provided the most consistent velocities in .223 and .243 and with .308 it did not matter. I choose to use .003. With cases where some or all of the brass has been work hardened enough to display springback after sizing I go with .004 to allow for the springback so the brass ends up at what most shooters and myself call .003 to .004 neck tension. I chamfer the mouths, do not use any lube and never had any copper shave off yet.
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I think some folks forgot a zero: .0005 inch instead of .005 inch.
You can make a tool to measure bullet pull force with a hand scale and collet style bullet puller.
Remove die from your press then put a cartridge in the shellholder, top it out, tighten collet on bullet, attach the scale then pull the bullet reading the scale. Do several to get average.
Military 7.62 NATO match ammo bullet pull spec is 20 pounds minimum, 60 pounds minimum for most service ammo.
You can make a tool to measure bullet pull force with a hand scale and collet style bullet puller.
Remove die from your press then put a cartridge in the shellholder, top it out, tighten collet on bullet, attach the scale then pull the bullet reading the scale. Do several to get average.
Military 7.62 NATO match ammo bullet pull spec is 20 pounds minimum, 60 pounds minimum for most service ammo.
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ok typo corrected and if you want to jump through hoops for some number that is probably impossible to duplicate that's your business. I'll keep using the definition that most the reloaders out there use and that is easily duplicated. If I tell you my neck thickness is .014 thick and I use a .289 bushing you can duplicate my neck tension by turning your necks to .014 and using a .289 bushing. Simple and effective
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For what it's worth, most military rifle cases are made with neck inside diameter about a thousandth inch or so larger than bullet diameter. Would they have a minus neck tension?
If several people use .003 inch "neck tension" across different lots and dimensions of case necks, bullet pull forces will vary from lot to lot.
If several people use .003 inch "neck tension" across different lots and dimensions of case necks, bullet pull forces will vary from lot to lot.
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it's really pretty simple - bushing diameter minus neck wall thickness multiplied by two and subtracted.
example .289- (.014 x 2) = .261, bullet OD is .264 or .003 larger. or
290 - (.014 x 2) =.262 bullet = .264 or .002 larger
You can change bushings or turn neck brass to adjust to get the tension you prefer.
or https://forum.accurateshooter.com/threads/turning-necks-for-standard-fl-dies.4019066/
or use a Lee collet die and tune it like John Keilly does
https://forum.accurateshooter.com/threads/lee-collet-die-experience.3885018/#post-36644901
or just get a non bushing die, size the case then seat the bullet and shoot
images of bowling balls on ramps, cats in bird cages and fans knocking over books in a domino effect comes to mind - Rube Goldberg would be proud
example .289- (.014 x 2) = .261, bullet OD is .264 or .003 larger. or
290 - (.014 x 2) =.262 bullet = .264 or .002 larger
You can change bushings or turn neck brass to adjust to get the tension you prefer.
or https://forum.accurateshooter.com/threads/turning-necks-for-standard-fl-dies.4019066/
or use a Lee collet die and tune it like John Keilly does
https://forum.accurateshooter.com/threads/lee-collet-die-experience.3885018/#post-36644901
or just get a non bushing die, size the case then seat the bullet and shoot
images of bowling balls on ramps, cats in bird cages and fans knocking over books in a domino effect comes to mind - Rube Goldberg would be proud
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