Neck expansion

Shoulder angle can contribute to neck tension when FL sizing necks (which nobody should ever do)(ever).
But on bumping itself, I've yet to see an actual standard with which it occurs. It can be angular, rolling shoulders to a lower angle. It can be a push at neck-shoulder junction, or at shoulder-body junction, or mid-shoulder. Any suffice to function for chambering, and I'm sure it happens every kind of way as an abstract.
 
I wanted to go over another matter about neck expansion. The 'why do it' part.
Up front, I'm not a metallurgist, so I can only generally describe this.
When we size brass(in any way, anywhere) we're adding energy. The brass is no longer in it's lowest energy state and it wants to get back there. Spring back is an immediate evidence of this, but what many don't consider is that spring back energy does not reach a balance all at once. There is more of it in play, over a longer period of time (way slower rate).

Brass continues to move (where it can) opposite of last energy added. If it is not allowed to move, it will just always want to, holding a bias of energy. So, when we decide to skip expansion as a last action, we're leaving necks sprung back outwards, and biased to continue creeping outward. If your sizing provided the interference you wanted right off the bat, it won't be like that a month from now. And your shoulder bumps will change, and so will your primer seating.

Consider why we have always expanded necks, as a standard.
When you make ammo today, for later use down the road, you should expand necks (what I call pre-seating).
With this bias set, necks will tighten down the road, or at least grip bullets with the same force, instead of a lowering force. I'm sure ammo makers have been aware of this for longer than most of us have been alive.

I mentioned earlier that pre-seating expansion would ideally take necks to cal, and released to spring back into ~1/2thou interference. This is not only ready for bullet seating, but an incredibly stable condition.
When you seat bullets in these necks, they will expand necks only against spring back, and there will be no up-sizing (no yielding). The inward spring back bias is locked, unchanged, right there. Perfect.
You could rely on this today, and weeks, months, years down the road.

A really good process anneal (stress relieving) is effective to remove much of this character in brass. But of course this changes what you get from brass (it's character), so it is only a good thing while it tests as such.
Annealing is not a fix-all.
While annealing increases seating force, it lowers neck tension forces. So for example, if your load likes high neck tension, then it can punish you for an annealed condition.
You want stability, and to load develop with it, and be able to manage it.
I've found that it's easier to manage through minimal sizing, but a good annealing plan may work as well for you.
With a cartridge that has to be sized a lot, like a 30-06 for example, then I would plan up front for frequent dip annealing.
 
Well, quick update....
I'm loading 300 WSM, Win brass, neck turned to 0.013 thickness. Fired neck runout is about 0.0017".

From my Forester FL die with expander this brass will FL size to CBTD fired -0.0015 with a neck runout averaging 0.0013."

I ran some through my Redding type S die with floating carbide expander. It gave me 0.003" runout. I measured the decapping rod and it had a little over 0.001" runout and had more runout in the decapping pin. I ordered a new one.

Next, I want to try multiple sizing steps with the Redding die and with/without expander in the die. Also will try expanding on my k&m mandrel.

Last, the very tips of my case necks curl in to a smaller diameter. Anybody know why? Not hitting end of the chamber? I'll have to look in there with my borescope...
 
Well, quick update....

Last, the very tips of my case necks curl in to a smaller diameter. Anybody know why? Not hitting end of the chamber? I'll have to look in there with my borescope...
I've witnessed this several times. Most times your bore scope will reveal carbon in the case mouth end of the chamber. Not enough to impinge on bullet release or chambering but with "spring back" it will return to slightly less than bullet diameter.
A second cause seen once in a rechamber was "shadow" of the old chamber allowing the rear of the neck to expand a tiny bit (less than 2 tenths of a thou). Don't know why but outside turning another 1/2 thou stopped it.

My first inspection on all fired brass is checking case mouth with a new bullet. Finds the neck carbon issue everytime.
 
With all annealed & neck turned brass.....

So, here I sit with Forster FL die giving 0.0015" average runout and 0.002" neck tension.

I tried my Redding FL die with expander and got 0.0035" runout on some brass....average over 0.002".

i tried without the expander, using a second k&m expander....0.0025" ahhh

I tried locking the bushing down with a straight case.....0.0015" avg runout. Not bad, but no expander and 0.001" neck tension....enough?

I think I will do 10 Redding locked down and 10 Forester sized and shoot comparison groups. Also look at how the bullet seating looks.
 
0.001" neck tension....enough?
For now, but after a few loadings, i had to use a .001" smaller bushing on neck turned 243 brass. A few out of the lot didnt have a good grip on the bullets.

Annealing may make a difference? I dont anneal.
 
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