Following up on another thread "how to measure neck tension", I wanted to go past apparent consensus that use of 'neck tension' as a misnomer is appropriate. It's just my belief that fallacies should not be perpetuated.
To begin, neck tension is not interference fit, nor represented directly(often no correlation) by seating/pull forces.
Another misunderstanding about the action of tension is seen with those believing we need a measure of 'pull force'.
Neither seating force nor the same as pull force hold's direct meaning about tension. These terms amount to no more than friction. You can affect seating friction many ways with no affect to MV at all. Yet you can measure the affect of an actual tension change with 1/16" change of length in neck sizing. This is because bullets are not pushed out of necks by pressure. They are released by necks expanding under pressure(even if only ~.0000001 over cal).
Bullet release is a matter of overcoming grip -not friction.
So what is grip?
The grip on your bullets amounts to spring back of the brass for the area applied(against seated bullet bearing).
Spring back of necks is typically 1thou for normal hardness, up to 2thou for extremely hard/brittle brass. That's it, and it's plenty enough. Normal spring back against .250" length of bullet bearing will provide more tension than against .125" of bearing. This is your partial neck sizing adjustment of tension. Grip of a given length is different for 22cal than 30cal.
With FL sizing of necks you can get more tension, a lot more tension, all the way to extreme and dangerous(depending on donut & seated bearing). This presents the potential to size length greater than seated bearing, and this extra length influences spring back that actually is against bearing. But other than achieving greater tension, I see more bad than good in FL sizing of necks, especially w/regard to tension variance. If you size way past seated bearing length, including donut area, well you've dramatically increased tension AND tension variance. Fine(and often desired) for a tiny 6PPC,, bad for a 7WSM.
So when a point blank BR shooter insists that 4thou under cal(interference) is magic with his 6PPC or 30BR, you need to understand that your LR cartridge is not a 6PPC, and that running typical ~75Kpsi+ competitive 6PPC pressures is not viable for you. He was probably FL neck sizing. While YOU'RE partial neck sizing, 4thou under is nothing more than overworking of necks anyway.
Try this:
Measure a neck OD as smoking from your chamber. Way undersize the neck for no more than seated bearing length. Let's say 5thou under cal. Seat a bullet, noticing the additional effort needed. Then pull that bullet and again measure the neck OD. You'll find that your seated bullet expansion sized the neck(which is bad), and that the neck sprung back ~1thou under cal. That is your tension(hoop tension, grip). It will do the same whether you size down 1thou or 10thou.
The only time this changes(in a single sizing action) is when you had sized beyond the length that the seated bullet bearing was able to reach/re-expand.
As far as measuring tension, there is currently no tool on the market to do this. If there were it would work something like a hydraulic expander inserted in a neck, which is between a v-block & indicator. We would turn up the pressure to expand the neck ~1thou and take a reading in PSI. When we released the pressure the neck would fully spring back(unless over annealed).
Seating force measure, if friction managed carefully, can provide a comparative measure that indirectly corresponds to tension variance, but we've been assigning too much credit to this IMO.
Frequent process annealing often increases seating force/friction but reduces actual tension. Not a bad thing if your load likes low tension, and lower tension also means lower variance of it. That doesn't mean it's best for everyone.
I'm a partial neck sizer(Wilson), and use bushings to achieve 1thou under cal after spring back and pre-expansion with a mandrel. Tension for me, even as a relative unknown in quantity, is useful, in that I can tweak tune with it -as sizing length. You don't here anyone talking about that, but there it is..
I'm not out to attack our notions, but to help with understanding about tension itself.
To begin, neck tension is not interference fit, nor represented directly(often no correlation) by seating/pull forces.
Another misunderstanding about the action of tension is seen with those believing we need a measure of 'pull force'.
Neither seating force nor the same as pull force hold's direct meaning about tension. These terms amount to no more than friction. You can affect seating friction many ways with no affect to MV at all. Yet you can measure the affect of an actual tension change with 1/16" change of length in neck sizing. This is because bullets are not pushed out of necks by pressure. They are released by necks expanding under pressure(even if only ~.0000001 over cal).
Bullet release is a matter of overcoming grip -not friction.
So what is grip?
The grip on your bullets amounts to spring back of the brass for the area applied(against seated bullet bearing).
Spring back of necks is typically 1thou for normal hardness, up to 2thou for extremely hard/brittle brass. That's it, and it's plenty enough. Normal spring back against .250" length of bullet bearing will provide more tension than against .125" of bearing. This is your partial neck sizing adjustment of tension. Grip of a given length is different for 22cal than 30cal.
With FL sizing of necks you can get more tension, a lot more tension, all the way to extreme and dangerous(depending on donut & seated bearing). This presents the potential to size length greater than seated bearing, and this extra length influences spring back that actually is against bearing. But other than achieving greater tension, I see more bad than good in FL sizing of necks, especially w/regard to tension variance. If you size way past seated bearing length, including donut area, well you've dramatically increased tension AND tension variance. Fine(and often desired) for a tiny 6PPC,, bad for a 7WSM.
So when a point blank BR shooter insists that 4thou under cal(interference) is magic with his 6PPC or 30BR, you need to understand that your LR cartridge is not a 6PPC, and that running typical ~75Kpsi+ competitive 6PPC pressures is not viable for you. He was probably FL neck sizing. While YOU'RE partial neck sizing, 4thou under is nothing more than overworking of necks anyway.
Try this:
Measure a neck OD as smoking from your chamber. Way undersize the neck for no more than seated bearing length. Let's say 5thou under cal. Seat a bullet, noticing the additional effort needed. Then pull that bullet and again measure the neck OD. You'll find that your seated bullet expansion sized the neck(which is bad), and that the neck sprung back ~1thou under cal. That is your tension(hoop tension, grip). It will do the same whether you size down 1thou or 10thou.
The only time this changes(in a single sizing action) is when you had sized beyond the length that the seated bullet bearing was able to reach/re-expand.
As far as measuring tension, there is currently no tool on the market to do this. If there were it would work something like a hydraulic expander inserted in a neck, which is between a v-block & indicator. We would turn up the pressure to expand the neck ~1thou and take a reading in PSI. When we released the pressure the neck would fully spring back(unless over annealed).
Seating force measure, if friction managed carefully, can provide a comparative measure that indirectly corresponds to tension variance, but we've been assigning too much credit to this IMO.
Frequent process annealing often increases seating force/friction but reduces actual tension. Not a bad thing if your load likes low tension, and lower tension also means lower variance of it. That doesn't mean it's best for everyone.
I'm a partial neck sizer(Wilson), and use bushings to achieve 1thou under cal after spring back and pre-expansion with a mandrel. Tension for me, even as a relative unknown in quantity, is useful, in that I can tweak tune with it -as sizing length. You don't here anyone talking about that, but there it is..
I'm not out to attack our notions, but to help with understanding about tension itself.
