You and Mikecr bring up something that's been bothering me, and maybe it shouldn't be. I'm noticing that when I use a Redding bushing-style FL die to bump shoulders back by .003, only about 40% of the neck is sized. I've been thinking that would potentially give rise to inconsistent neck tension and potentially more inconsistent runout, which could have a negative effect on consistent precision. Are you fellows saying this is both normal, and positive?Talking of consistency with IF, the most drastic thing for me, besides annealing after every shot before sizing, is using powdered graphite on the insides of my necks. My ES/SD shrunk doing this and velocities became slightly less.
I HBN coat my solid CNC turned 323g .338” bullets for my 338-416 Rigby, and the velocity in that rarely alters by 8fps, which is the lowest ES of any of my rifles, including my high end comp F-class guns, which average in the low teens.
The only 2 cartridges I size 85-95% of the necks are my 264WM & 300WM.
I find neck length has little to do with Precision. My 25-06 that I use in Hunter comp shoots extremely well with .180-.200” of the neck sized with 115g Berger Hybrids, this just shows that at .003” IF, this is sufficient to keep bullets straight while just kissing the rifling, maybe .002” into the rifling proper.
My 22-250AI is similar, only needs .200” of bullet bearing in the neck.
I hear most people shooting for .002-.003 interference but as long as I can push a bullet tip on a loaded round against the bench as hard as I can and it doesn't move, I'm usually happy as long as your dies are not overworking the necks of the brass.
Had a resize die that sized the necks down about .008 before they were pulled over the expander. Led to neck splits on 2nd or 3rd reload.
Today, find myself agreeing with your thoughts more and more. As Mike cr pointed out, neck tension alone is tough to measure.You and Mikecr bring up something that's been bothering me, and maybe it shouldn't be. I'm noticing that when I use a Redding bushing-style FL die to bump shoulders back by .003, only about 40% of the neck is sized. I've been thinking that would potentially give rise to inconsistent neck tension and potentially more inconsistent runout, which could have a negative effect on consistent precision. Are you fellows saying this is both normal, and positive?
Here's my concern, and apologies to others when it gets a little technical, but in threads about how many rounds to shoot when developing a load, it's clear that smaller sample sizes give rise to more variability, and a larger sample size gives a better level of confidence that the conclusion you're drawing is actually valid. I'd apply that same logic to this issue, and assert that the greater length of the neck that you size, the less variability in neck tension you'd see. And remember, my point is not about total neck tension, I'm talking about the variability of that tension. The increase in neck tension from having a larger area gripping the bullet can be adjusted by using different neck bushings or expander mandrels.
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On a separate question, let me push back a little on the question of neck tension not being the same as interference (friction) fit. As an engineer I would concede that seating friction is a parametric indicator of neck tension. For normal people (non-techies), I mean that even if we can't directly measure neck tension, we can measure the seating force due to friction, and that then gives us a relative indication of neck tension, even if we're not measuring it directly. Parametric measurements are common in many disciplines and can give good results.
I use an LE Wilson seating die with an arbor press. I haven't spent the money for one, but some retailers offer a hydraulic arbor press with a pressure gauge that gives a readout of the frictional force when seating. I'll add a link and photo below. It seems to me, and I'd love feedback on this, pro or con, that the frictional seating force is directly related to neck tension, and measuring it would allow us to both obtain consistency, and adjust the neck tension to a desired level. Would this not be an effective way, even if it's indirect, to measure and adjust neck tension?
I might quibble a little about the photo, however. I wonder why the gauge reads almost 10 PSI when it's at rest, and I also wonder if a 100 PSI gauge has too much range for the relatively light seating forces involved with small calibers. A gauge with a range that is sized to provide results somewhere in mid-range will give more visible data than one which, for example, only moves off the peg by 10% when the same force is applied. I haven't used one of these so I'm only speculating, I don't know how much force it would take to seat different calibers. Maybe a 100 PSI gauge is needed for some of the big calibers, and a gauge with 0 - 25 PSI or 0 - 50 would be better for a 22 caliber, for example. If I ever buy one of these, I'll ask the company about that.
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Curious...What's the largest caliber and case capacity cartridge in your arsenal of rifles?You can't.
What Rick described is INTERFERENCE fit.
And seating forces are not tension either, but seating FRICTION.
Neck tension is the gripping force applied to an area of seated bullet bearing (in PSI).
We currently have no means to measure it.