How to measure neck tension
- Thread starter CHROME
- Start date
I will give you a perfect example: MINE! I have a .284 Win with a .313 neck. I had to turn my necks down to 12K neck wall thickness. I use a .308 Bushing. That bushing, with a seated bullet, allows for about a 3/4 thousandths neck tension as my outside neck diameter "bounces" on my RCBS micrometer, between 308.5 and 309. But in reality, since I don't have a 10K micro, it is about 3/4 thousandths tension.
Measure the OD of loaded round at the pressure ring if one exists. As an example, say .261" is your reading. A bushing that will give your unloaded case neck an OD reading of .260" is .001" of neck tension. A bushing that will give your case neck an OD reading of .259" is .002" of neck tension, etc, etc. Now be aware that .002" of neck tension is not equal neck tension in all circumstances. The thickness of the case neck will come into play. .002" neck tension on a case with a neck thickness of .014" is not equal to a neck tension of .002" with a neck thickness of .0086". So to say that you are using a .002" neck tension, by itself, means very little.
Neck tension On a bullet can very on the hardness of the case. Size neck tension is different and it is measured by size. Larry
deepwater said:
Thank you.
Keith Glasscock
Gold $$ Contributor
I measure the ID of the case neck prior to seating and I measure the force required to seat the bullet. Neither is neck tension per se, but gives me the information I need to get the ballistic consistency I need.
Keith Glasscock said:
+1
Few of us have a way to measure actual neck tension, but in reality it isn't important for most shooters. As pointed out by others, if you use a bushing type neck re-sizing die, the difference between the die size and the loaded round size is usually called "neck tension", even though it is an indirect way of measuring it. And, depending on the situation, it might not be very accurate either.
If you have an accurate way to measure case thickness (hint: not with a set of calipers) and bullet diameter, the sum of those measurements vs the loaded round diameter is usually considered a better way to measure neck tension.
As a practical matter, those who shoot rounds one at a time from a bolt gun will want pretty low tension, about .001", more or less. If you feed from a semi-auto magazine, you'll want more. But what you want more than anything is consistency. In my opinion, (and I'm not alone) you can achieve that best by annealing your cases each and every time.
Obviously, each time you shoot and resize a case, it work hardens and has more "spring back". That means a four-times fired case will have a different "tension" than round made from a freshly annealed case if you size them with the same die. For some, this is very important, for others .......... not so much.
If you have an accurate way to measure case thickness (hint: not with a set of calipers) and bullet diameter, the sum of those measurements vs the loaded round diameter is usually considered a better way to measure neck tension.
As a practical matter, those who shoot rounds one at a time from a bolt gun will want pretty low tension, about .001", more or less. If you feed from a semi-auto magazine, you'll want more. But what you want more than anything is consistency. In my opinion, (and I'm not alone) you can achieve that best by annealing your cases each and every time.
Obviously, each time you shoot and resize a case, it work hardens and has more "spring back". That means a four-times fired case will have a different "tension" than round made from a freshly annealed case if you size them with the same die. For some, this is very important, for others .......... not so much.
Without some extremely expensive gear, there is no means to quantify measurement of "neck tension".
However, if you are experienced in use of a bullet puller you can get some idea of relative resistance to obtaining release. There are factors involved beyond die neck or bushing diameter. Material of bullet jacket is one. Some gilding metal formulations may be different and have different ductile and tensile properties. As mentioned, the brass itself has properties. There is no standard for annealing in terms of achieving a uniformity from piece to piece. If you lube your case neck w/mica, use a fine brush, or tumble clean you affect the bullet gripping surface.
Uniformity of neck thickness, at least on initial loading, achieved by using quality brass or turning necks, along with a bushing die sizer gives about the highest degree of control. Collet sizer may have similar effect, especially if have a set of different sized collets. There is also potential with a taper-crimp die and the Lee Factory crimp die for achieving a more uniform bullet release tension.
If you study the Sierra Loading manual, you will see that most, if not all, "accuracy loads" are about median in terms of velocity. Typically, these won't require a crimp or great tension to produce their velocity level; except in large capacity magnum rifle loads, and then depending on powder burn rate chosen.
There is also a factor of ctg brass adhesion to gilding metal, maybe to lead alloy bullets also, but don't recall seeing it ever discussed there. Fact is, over time there is some electrolytic or other adhesion that creates a bonding effect between case and jacketed bullet. This will affect bullet release and likely impart variation in performance that cannot be controlled or anticipated.
If you make a dummy cartridge and use a kinetic puller with an educated "feel" for the bullet tension you are looking for; using a bushing sizer with range of bushings may enable verification of your effort. Perhaps the standard .001 difference in sizes is too gross for best work? Need to also be mindful of using a "sizing ball" that doesn't "correct" your bushing sizing efforts as decapping stem is removed from case neck.
Optimizing preparation of your brass will usually involve more than just selecting a bushing and going to work...
However, if you are experienced in use of a bullet puller you can get some idea of relative resistance to obtaining release. There are factors involved beyond die neck or bushing diameter. Material of bullet jacket is one. Some gilding metal formulations may be different and have different ductile and tensile properties. As mentioned, the brass itself has properties. There is no standard for annealing in terms of achieving a uniformity from piece to piece. If you lube your case neck w/mica, use a fine brush, or tumble clean you affect the bullet gripping surface.
Uniformity of neck thickness, at least on initial loading, achieved by using quality brass or turning necks, along with a bushing die sizer gives about the highest degree of control. Collet sizer may have similar effect, especially if have a set of different sized collets. There is also potential with a taper-crimp die and the Lee Factory crimp die for achieving a more uniform bullet release tension.
If you study the Sierra Loading manual, you will see that most, if not all, "accuracy loads" are about median in terms of velocity. Typically, these won't require a crimp or great tension to produce their velocity level; except in large capacity magnum rifle loads, and then depending on powder burn rate chosen.
There is also a factor of ctg brass adhesion to gilding metal, maybe to lead alloy bullets also, but don't recall seeing it ever discussed there. Fact is, over time there is some electrolytic or other adhesion that creates a bonding effect between case and jacketed bullet. This will affect bullet release and likely impart variation in performance that cannot be controlled or anticipated.
If you make a dummy cartridge and use a kinetic puller with an educated "feel" for the bullet tension you are looking for; using a bushing sizer with range of bushings may enable verification of your effort. Perhaps the standard .001 difference in sizes is too gross for best work? Need to also be mindful of using a "sizing ball" that doesn't "correct" your bushing sizing efforts as decapping stem is removed from case neck.
Optimizing preparation of your brass will usually involve more than just selecting a bushing and going to work...
fguffey said:
Is it possible to measure air pressure with a standard gage calibrated in psi, or do we need one calibrated in pressures? My gosh, the BS is flowing from the MENSA crowd.
Alex Wheeler
Site $$ Sponsor
You really cant measure it. All you can do is prep your cases all the best you can and pick a bushing that shoots best. I have played with the force gauges. The numbers do not correlate with accuracy.
zfastmalibu said:
Yes you are correct that we can not measure it directly, but we can set it to a standard from which to judge changes. Either more or less, as is needed. I believe that is what is referred to when folks discuss neck tension, not an actual number calibrated in "tensions" or pounds per sq inch. It is a reference we set, so that we can then work from that reference. It may measure 10K or .0001 on our imaginary scale. We can call it potatoes or tensions, it is a reference.
Jim Casey said:
"Yes you are correct that we can not measure it directly" I am correct, a reloader can measure bullet hold. A reloader can not measure tension, a reloader can pretend to understand neck tension. A reloader that can operate a bath room scale can measure bullet hold.
I want all the bullet hold I can get.
F. Guffey
Mr. Guffey, why not attempt to answer the OP question, rather than attempting to prove how you are right.
CHROME
Silver $$ Contributor
Thanks all.....only trying to see if the was I am doing it was inline with other folks steps and opinions. I have ordered quality calipers and mic for measuring wall thickness. I was trying to use calipers to measure thickness originally. I have since spoken to 3 manufactures of neck turners and have come to one conclusion....you have to be able to accurately measure wall thickness first.
CHROME said:
Right you are. When you shop for a neck turner, don't forget the 21st Century unit. Their cutter head along with their little cordless drill powered lathe is very nice. Not the cheapest but it's not the most expensive either and gives better bang-for-the buck than any of the units I looked at. It's accurate and very easy to use. I really like mine.
Alex Wheeler
Site $$ Sponsor
Men,
The neck expands to release the bullet. The bullet does not slide out of the neck. If it did the neck would not expand at all. Seating force is a very crude way of judging the grip a neck has on a bullet. Measuring before and after doesnt always tell the truth either as that will vary as the hardness of the necks change, but the grip seems to stay the same. Harder brass with less "tension" grips the same as softer with more "tension". Annealing makes a huge difference on how much neck tension the gun will want, and how much you can get.
The neck expands to release the bullet. The bullet does not slide out of the neck. If it did the neck would not expand at all. Seating force is a very crude way of judging the grip a neck has on a bullet. Measuring before and after doesnt always tell the truth either as that will vary as the hardness of the necks change, but the grip seems to stay the same. Harder brass with less "tension" grips the same as softer with more "tension". Annealing makes a huge difference on how much neck tension the gun will want, and how much you can get.
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