Questions about sizing with collet die

[Splat]

I've searched and didn't find it so here it goes.
How many times is it "safe" to neck size with the collet before bumping the shoulder back? Is it a matter of when accuracy goes or clambering problems?
Sizing Lapua 308 brass (no neck turning) with a Lee Collet die. I've loaded two times with this brass and I'm about to load the brass for the third time but not sure if I should FL size it. I'm still doing load development on a new gun so I can't say weather or not if the accuracy is decreasing.

I've been trimming to 2.005" and after collet cases are fired they measure 2.007"-2.008" and after I run them through the collet again, they grow to about 2.010"-2.011". Sound right?? I'm new to this neck sizing thing. Sorry if the questions are rather amateur. I thought if you neck sized you didn't need to trim that much.


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[29aholic]

Personally, once the cases are fire formed to my chamber I don't FL resize any more. I FL size new brass or brass fired out of another gun.

 

[Steel head]

Usually my cases start getting tight after about 5 firings and then I bump the shoulder back .001-.002.

 

[Fred_C_Dobbs]

The case grows in length because chamber pressure has stretched the brass. It's got nothing to do with how it was sized. The higher your Pmax, the more your brass is going to stretch.

Neck sizing in general is a benefit because it saves a little working of the case at the shoulder, and it preserves the fire-formed shape. Collet neck sizing in particular has the added benefit of reducing the working of the neck because it isn't first undersized, then stretched back out to the spec size, as it is when sizing with an expander ball. And it has better ID concentricity.

I let the rifle be the "shoulder bumping required" gauge. If the spent casing will re-chamber without undue force, it's GTG. When it starts getting a little tight, I bump the shoulder. I couldn't care less how many times it's fired before that happens. In fact, the more, the better. Putting it back in a full length sizer only would screw up your fire forming. I can't remember the last time I used a FLS die for a bolt gun reload.

From a safety standpoint, neck sizing is no different from FLS. The biggest concern is still case head separation. If you're having to trim frequently, you're probably also running a pretty high Pmax (or your brass is soft-ish). Which increases the risk of CHS.

The material that caused your case necks to lengthen had to come from somewhere, and that somewhere is the case head. Every time they're fired, if there's any increase in case length, that means the case head also got a bit thinner. You might see a shiny ring on the outside of the case...

... then again, you might not, ... until this happens ...

... which probably will ruin your boxers.

Which is why you probe the inner wall to feel for a corresponding inner groove. The inner groove is a much more reliable indicator of incipient CHS than the shiny ring. I use a high-dollar probe I made from a section of cut-up coat hanger. It's got a slight bend and a sharp-ish bevel on the testing end. I scape the inner wall with it, sometimes every firing, but at least every time the case requires trimming or the shoulder requires bumping.


EDIT:
I forgot to mention that leaving the case body fire-formed (by not full length sizing) reduces the tendency to CHS because it leaves you with minimal headspace. If you have anything more than minimal headspace, the next firing always will re-fire-form the case, which stretches the case body as it drives the shoulder back to its fire-formed length. So from a safety standpoint, substituting FLS for neck-only could actually be a bad thing. So I was a little off-base when I earlier wrote there was no difference.

 

[kansas]

I can usually go 5 times before bumping the shoulder back using Lapua brass. When I find a round or two out of a batch that is hard to close the bolt on then I bump. I also trim my brass to 2.010 and trim it every time to be consistent. Probably over kill but everyone has their way of doing things. I love the Lee collet die. Works great and gets runout down near zero.

 

[CharlieNC]

You can monitor with a headspace comparator, and watch for the case to grow as you neck size. At some point the case will likely become tight to bolt (yes, check before loading) and based on that measurement you will know as you approach this in the future to FL size.

 

[Splat]

The case grows in length because chamber pressure has stretched the brass. It's got nothing to do with how it was sized. The higher your Pmax, the more your brass is going to stretch.

Neck sizing in general is a benefit because it saves a little working of the case at the shoulder, and it preserves the fire-formed shape. Collet neck sizing in particular has the added benefit of reducing the working of the neck because it isn't first undersized, then stretched back out to the spec size, as it is when sizing with an expander ball. And it has better ID concentricity.

I let the rifle be the "shoulder bumping required" gauge. If the spent casing will re-chamber without undue force, it's GTG. When it starts getting a little tight, I bump the shoulder. I couldn't care less how many times it's fired before that happens. In fact, the more, the better. Putting it back in a full length sizer only would screw up your fire forming. I can't remember the last time I used a FLS die for a bolt gun reload.

From a safety standpoint, neck sizing is no different from FLS. The biggest concern is still case head separation. If you're having to trim frequently, you're probably also running a pretty high Pmax (or your brass is soft-ish). Which increases the risk of CHS.

The material that caused your case necks to lengthen had to come from somewhere, and that somewhere is the case head. Every time they're fired, if there's any increase in case length, that means the case head also got a bit thinner. You might see a shiny ring on the outside of the case...

... then again, you might not, ... until this happens ...

... which probably will ruin your boxers.

Which is why you probe the inner wall to feel for a corresponding inner groove. The inner groove is a much more reliable indicator of incipient CHS than the shiny ring. I use a high-dollar probe I made from a section of cut-up coat hanger. It's got a slight bend and a sharp-ish bevel on the testing end. I scape the inner wall with it, sometimes every firing, but at least every time the case requires trimming or the shoulder requires bumping.


EDIT:
I forgot to mention that leaving the case body fire-formed (by not full length sizing) reduces the tendency to CHS because it leaves you with minimal headspace. If you have anything more than minimal headspace, the next firing always will re-fire-form the case, which stretches the case body as it drives the shoulder back to its fire-formed length. So from a safety standpoint, substituting FLS for neck-only could actually be a bad thing. So I was a little off-base when I earlier wrote there was no difference.

Thanks for the in depth explanation. That really helps a lot. I've only been working loads so far with this brass. I have two untouched boxes of Lapua that I will fire form once I find a few pet loads and I will take your advice and try clambering before loading the next load with the current brass.
Thanks again.



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[29aholic]

Just so you know, the "Pet Loads" you work up in multi-x fired cases may not necessarily be as good.

 

[918v]

I bump the shoulder .002" for every loading because I don't like to grind the bolt lugs against the lug recess. I like the nice smooth crisp bolt closing action. But I'm not looking to get 30 reloads out of a case either.