Question about full-length sizing dies?

1
Ok, I can often over think things.

But exactly what is a full- length sizing die supposed to accomplish? It sizes the full-length that's a circular argument.

I take a fired case and use that die. Is it supposed to, depending on where I set it, push the case from top to bottom allowing me to set the case length into spec? Or is it messing with the case diameter in a way I can't fathom?

Is it supposed to, depending on where I set it, smoosh the case back down to a pre-fired state? I don't think so but it crosses my brain.

To add to the complication, I've read that a case fired through a particular rifle expands to fit the rifle's chamber so just needs neck sizing.
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Re: Question about full-length sizing dies?

2
I'm no expert, and I'm sure others will have more/better info to add. But I'll answer anyway cause why not.

The case expands to fit nicely into the chamber of the rifle that fires it, the full length die squeezes the case back into spec. Neck sizing is great for target shooting brass that's only ever going to be used in one rifle, it can help the brass last longer and your brass is the perfect fit for your chamber. The case elongates during the sizing (more with full length than neck sizing) and when it gets too long you trim it back down to be within spec.

Neck sized brass might not chamber in a different rifle from the one that fired it last. Most of the people I've talked to recommend full length sizing for hunting because it's one less thing to go wrong.

And a picture!
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Re: Question about full-length sizing dies?

3
Pretty spot on, but to add: Full length resizing does several things to the brass. Outside of the neck sizing, it also pushes the shoulder back into spec, as well as restoring the brass diameter on the body to spec. Because of the squeeze, you also elongate the brass, as it has to flow somewhere, so that's why the trimming after resizing. (Or close to it anyway) neck sizing is excellent for bolt rifles where you use the same brass in the same rifle each time, as the case is fire formed to the rifles chamber. You can just restore neck tension to hold the bullet, giving you longer brass life, since there is much less work on the brass, reducing thinning which is one of the main causes of case failure.

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Re: Question about full-length sizing dies?

7
The neck dies still have an expander ball- otherwise you could lose concentricity when the die squishes the neck back down to size.

A point of note, it's not recommended to neck size for semi-auto rifles. With a bolt action you can still chamber a tight round, with a semi you could wind up locking up the rifle badly.
“Do the best you can until you know better. Then when you know better, do better.”
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Re: Question about full-length sizing dies?

8
Thanks for the replies!

So if I'm reading this correctly, the die squeezes the case back to the specified diameter. During this squeeze the case can get slightly elongated and may require trimming.

Or in the example of my 6.5X55 Swedish Mauser, the one rifle I own in that caliber, I can just neck size.

Or another example - if I segregate my .303 British brass by which of my two Enfields fired it, I can just neck size.

Comments?
Heller and McDonald are precedents to be followed, not obstacles
to be overcome

Re: Question about full-length sizing dies?

9
Correct. Now that said, eventually you may have to trim at some point, but because you are moving much less brass around, it will be way less often. And definitely don't mix the two sets of brass up! Will definitely result in some issues with the different sized chambers.
“Do the best you can until you know better. Then when you know better, do better.”
- Maya Angelou

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Re: Question about full-length sizing dies?

10
shinzen wrote:The neck dies still have an expander ball- otherwise you could lose concentricity when the die squishes the neck back down to size.

A point of note, it's not recommended to neck size for semi-auto rifles. With a bolt action you can still chamber a tight round, with a semi you could wind up locking up the rifle badly.
Actually, not all neck dies have expanders. Bushing dies simply compress the neck a specific amount based on the bushing size. Lee's collet neck sizer squeezes the neck down on a mandrel. Neither pulls on the neck the way a FL die does.

Edit. If you want to FL size the case w/o the neck stretching tug of the expander, you can remove the decapper/expander and use a Lyman M series expander. Its worked well for me for lots of rounds.
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