i have just recently started neck sizing cases and i have found a puzzling situation that i hope someone can explain to me.

i am dealing with 7mm Mauser cases by R-P. i have taken several fired cases and full length re-sized them. after full length re-sizing, the cases measured about 2.232" or so. then, I trimmed them on a Wilson trimmer to a length of 2.230". i fired these rounds and figured i would now neck size them. i measured several of them before i began the neck sizing. here's the strange part. the cases, after firing, measure 2.226" to 2.229". how is it that the cases shortened during firing?? as a matter of additional interest, the case headspace measures 1.785" before AND after firing. this measurement is made using a Hornady headspace gauge.

here is my thought... i am shooting a pretty mild load using a 140 grain bullet at 2,400fps. i think that the cases are swelling to fill the chamber, but that the load is not strong enough to stretch the case lengthwise after it swells to grasp the chamber wall. therefore, if the neck does not stretch, and the case does swell, it must shorten the overall length in order to fill the chamber.

am i making any sense or is there another answer? thanks for any help you might be able to give. i never had these kind of questions until i started measuring stuff. i just loaded 'em and shot 'em and was happy. now i am confused. anyway, thanks for the help.

Think of a balloon. You compress it in one direction and it grows in the opposite.
When you fire your cartridge the brass expands filling the chamber. The extra brass to do this comes from the length. Running it through your sizing die compresses the case walls back in place and the excess now squirts up the length of the case.
One good reason to always trim after resizing.

thanks, Joe. so does the reverse work also? is that why the fired cases come out shorter than they went in? they expand to fill the chamber and the brass used to fill the chamber comes from what would have been an increase in length if i was using a hotter load. since the hotness of the load doesn't cause the brass to stretch forward, it shrinks back to allow the brass to stretch to fill the chamber. i suspect it is. whaddaya think?

The cases were new, and after firing, they have conformed to your chamber.

Saeed...i understand what you are saying, but, the cases were once fired and full length re-sized, and trimmed to 2.230" before they went into the chamber. the cases came out of the chamber, after firing, and they were 0.004" shorter than they were when they went into the chamber.

i think this is a matter of little consequence. i have just never paid attention to case length as much as i now do and i was very surprised to see the cases come out of the chamber shorter than they were when they went into the chamber. i am used to cases stretching when fired. these shrunk. thanks again for your input.

quote:

i am dealing with 7mm Mauser cases by R-P. i have taken several fired cases and full length re-sized them. after full length re-sizing, the cases measured about 2.232" or so. then, I trimmed them on a Wilson trimmer to a length of 2.230". i fired these rounds and figured i would now neck size them. i measured several of them before i began the neck sizing. here's the strange part. the cases, after firing, measure 2.226" to 2.229". how is it that the cases shortened during firing?? as a matter of additional interest, the case headspace measures 1.785" before AND after firing. this measurement is made using a Hornady headspace gauge.

It is not doable, case length is most difficult for most reloaders to keep up with, it neither drives me to the curb nor does it lock me up, it is just one of those things I have to deal with.

Then there is the other length, that is the length of the case form the shoulder to the head of the case. most reloaders confuses this measurement with 'HEAD SPACE'. My cases do not have head space because SAAMI says the case does not have head space.

I form cases, some cases I form shorten ion length from the mouth of the case to the head of the case .045", for me? That is the cost of doing business. If I do not like the short case I can use longer cases. Instead of 30/06 I can use 280 Remington or 270 Winchester 'OR!' cylinder brass, cylinder 30/06 type cases are 2.650 long from the mounth of the case to the case head and? they do not have head space.

When I form 30 Gibbs the case body fills the chamber and forms the shoulder, keeping up? The pressure can not build is the case is expanding, while the case expands the case can not lock onto the chamber, and that is the reason the case shortens in length form the case mouth to the case head, when the case forms it pulls the neck back, part of the neck becomes part of the shoulder or the case.

I have always thought scribing the case body/shoulder juncture was a good ideal. reloaders have convinced themselves it is not...a good idea.

G. Guffey

quote:

i have just never paid attention to case length as much as i now do and i was very surprised to see the cases come out of the chamber shorter than they were when they went into the chamber.

There are reloaders that have began to take themselves more seriously than ....I take them. I keep asking them: "Is there a possibility you are leaving something out" "Your sequence of events is in a neat and tidy little bundle 'BUT!' there are times the sequence of events have nothing to do with what I am doing"

I have fired cases that were .127" shorter from the shoulder to the head of the case than the chamber from the shoulder to the bolt face, nothing, I eject cases that have no neck and short shoulders.

F. Guffey

You are over-thinking this; spend more time loading and shooting and less thinking about it. As long as your brass is not too long; that is the important thing.

A fired case is forced to take the 'long' route and conform to the chamber's corners at the neck. New bottleneck brass will usually and up shorter the first time fired.

He is right; firing makes them shorter; sizing them makes them longer. Usually. In straight walled cases; less.

I have experienced the same with new Norma brass in my 30-06. The chamber of the rifle is larger than other brands and therefore it cause the cases to stretch maximum inside the chamber and thereby decrease the overall length of the case. I therefore intend to necksize for at least the next 2 reloads.

well i appreciate the comments from everyone. thanks for the info.

Neck sizing and especially full length sizing can really lengthen the case.This is why cases need to be measured for trimming and OAL after they are sized.Cases keep on getting wider as you fire them and sometimes a little longer.When you full length size them again after a few firings they get really long and need trimming.