SIMPLE question on neck tension

[Wolf76]

Agree with RAMMAC.
I typically start with 1.5-2 thousandths of grip and keep carbon in neck.

 

[DocDoc]

And, at some point you are simply expanding the brass case with th bullet. At that point making the case neck smaller would not increase the force/strength the bullet is held by the case.

The other way to change the "hold", is to change the length of the sized neck. Size more of the neck and you have more of the neck gripping the bullet.

 

[Mikecr]

This isn't rocket science.
The bullet's diameter should be a couple of thousandths bigger than the inside diameter of the case neck. The more the difference the tighter the fit.

You're right in that it isn't rocket science, but your notion here is wrong. What you're describing is a common 'interference', which is different and independent of 'tension'..

Neck tension is spring back FORCE available to grip an AREA of seated bullet bearing.
It's unit of measure, if we did so, would be pounds per square inch (psi).
We adjust tension through spring back force(like with annealing), and area of grip(length of neck sizing and seating depth). If you think otherwise -you're wrong.

While neck sizing length is within seated bearing length, a setting of neck interference beyond full spring back(~1thou), provides nothing further for bullet grip. All you're doing with that is forcing seated bullets to expand necks to what they will be regardless. In other words, it matters not whether we pre-seat expand necks with a mandrel, or expand just the same with bullets.
The only thing holding that bullet bearing is the force provided by neck spring back, which is freely ~1thou max, for a portion of or full seated bearing length.

What this means is that if you set sized/sprung back necks, which are of normal hardness, to 1thou interference, for the full length of seated bearing, you have set maximum controlled neck tension.
Now, if you chose to size a length exceeding seated bearing, or including shoulder/donut in tension. then you get into uncontrolled tension. This is way higher, and varies a great deal. Nobody should ever do this.

On seating forces varying with neck hardness, friction, and expansion force, this means nothing directly about tension, and so it does not directly affect muzzle velocities/pressure.
To use seating force for comparative tension indication, you have to first normalize friction and seating expansion.
This, isolating neck hardness (force) and seating length (area) for indication.

 

[sturner]

All I do is to get as close to the same neck tension with every load

 

[Tree Farmer]

Mikecr, Your description of neck tension would suggest that bushing dies that can reduce neck diameters by increasing increments basically does not change the resulting neck tension since it is always set by the seated bullet. This suggests that a bushing die with different sized bushings is unnecessary since they really don't accomplish anything. Did I understand this correctly?

Could you expand on uncontrolled tension regarding shoulder/donut sizing?

 

[243winxb]

I tested 45 acp with different brands of brass, same expander button. Brass will spring back differently on each. Took any where for 40 lbs to over 100 lbs to seat. The 5.56 minimum is 35/45 lbs to pull. Federal & military spec. Roughtly .002" NT.

https://www.handloadersbench.com/fo...h-com-load-data/27215-neck-tension-experiment

 

[Mikecr]

Mikecr, Your description of neck tension would suggest that bushing dies that can reduce neck diameters by increasing increments basically does not change the resulting neck tension since it is always set by the seated bullet. This suggests that a bushing die with different sized bushings is unnecessary since they really don't accomplish anything. Did I understand this correctly?
Could you expand on uncontrolled tension regarding shoulder/donut sizing?

What we need from bushing neck sizing and follow-up expansion is no more than 1thou interference to cal (which can take a bit of trial & error to actually achieve), and desired neck sizing length (area to grip). With a given bushing you can adjust neck tension by adjusting length of neck sizing.
Bushing dies make this easy, and if you go no more than needed here, your neck induced runout can be kept very low, and work hardening can be reduced to minimum.

On uncontrolled tension:
Consider a neck FL sized with bullet bearing seated ¾ that length.
The interference is expanded only by that seated length, with the rest unexpanded and representing a lot of stored energy.
Now the energy contains not just that of partial length sized & well above donut area, but everything available, and it's binding (angular) on the bullet's base-bearing junction.
'Everything available' here is partial neck length + donut brass + expansion resistance of shoulder. That's significantly more variables and it's force is way beyond partial length sizing against only bullet bearing. That's why I coin it as uncontrolled.

There are underbore cartridges that love extreme starting pressures. So much so that they reward well beyond the negatives in high neck tension variance.
These are not hunting capacity cartridges though. They are things like 6PPC, 30BR, 30wolfpup (neckless).

 

[Tree Farmer]

Thanks for the clarification! I had to read it three times, but I understand your point. You've got me reconsidering my normal sizing procedure.

 

[Mikecr]

Don't overlook the potential for more consistent load tuning -> with proper neck sizing
And don't fall into a notion that greater tension will improve results. After all, lower neck tension = lower variance of it.

Hopefully your bushing die allows adjustment of sizing length.
I use Wilson inline dies. These happen to allow easy sizing length adjustment with shims.

I keep all reloading gadgets in a box for each barrel.