neck sizing and case stretching


November 14, 2012, 01:21 PM
I started loading my first and only "neck size only" case a while back for a bolt rifle in 7mm-08, using the Lee collet die.

I started with Privi factory loads and am on my second reloading.

The case length is still within spec. which has me wondering.....

If I neck size only this brass and only shoot it in the same rifle, will I eventually have to trim the brass?

Or is case stretching caused more by full length sizing, where the shoulder is repeatedly pushed back and then fire formed to the chamber?

Inquiring minds want to know :)

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November 14, 2012, 01:30 PM
Or is case stretching caused more by full length sizing


I load a lot of 7mm-08 in the same manner, for my wife.

After the initial fireform, I've not had to trim anything yet- and I'm starting to get splits finally....... so its been a while.

Same experience on my .308.

The only ones I've had to re-trim, are the ones that didn't form fully on the first attempt, or ones that wouldn't re-chamber after loading and unloading them for some reason...essentially starting the process over again.

I reason that its possible to load and fire it often enough that some brass migration would still occur...but its going to be an awful lot of firing... and nothing is going to match the migration of your first firing. Personally, I doubt your necks would take it that long.

November 14, 2012, 01:34 PM
Brass will still stretch from brass flow on firing but its a much much slower than the elongation you get by squeezing a case back into spec in a FL size die. Id say easily 90% of case lengthening is caused by the FL die.

An enlightening experiment is to measure fired cases before and after FL resize

The phenomena you're witnessing is actually one of Lee's selling points for their collet neck die

posted via that mobile app with the sig lines everyone complaints about

November 15, 2012, 02:12 PM
You'll still get some stretching, just not nearly as much as with FL sizing, and more so within the first several reloadings. The case will probably fail long before they will exceed SAAMI max.


November 15, 2012, 02:24 PM
No expander ball to work the brass, this is a good thing. Lee collet die.

November 15, 2012, 02:38 PM
There is stretch, there is flow, then there is that part where the imagination takes over, I have never found skid marks on the outside of a case, in the absence of skid marks on the outside of the case I assume brass does not flow on the outside, then there is the ‘dreaded?’ do-nut. Do-nuts, a most boring subject.

Then there is the pulling of the sizer ball/plug through the neck when the ram is lowered. The last time I discussed sizing, loading and firing one case 47 times I asked the shooter, sizer, firer of the one case fired 47 times what the case weighed before he fired it the first time. Back to stretch and or flow, or is it both? Not on the Internet but in the real world a real reloader/shooter fired one case so many times the case body thickness measured .0025 thick, I offered to form 200 cases for him if that was the only case he had. I did tell him I was surprised the case head did not pull off when when he lowered the ram ‘if in fact he was sizing the cases, he could have been pretending to be a bench rester’, still again, the bolt must cam/rotate to pull the case out of the chamber, he was not happy when the case was pulled apart for measurement.

F. Guffey

November 15, 2012, 03:44 PM
You'll eventually have to f.l. size the brass, in order to bump the shoulder.

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