Thread: Case lengthening when bump sizing

Before I launch into this , I'd first like to apologise to @knightshade for derailing his thread with this topic. Sorry .

I'd also like to say that this thread is in no way meant to be preachy or argumentative , ust for discussion .I'll try to get the tone right .

Okay, so this seems to be a relatively common phenomena and the question has appeared a few times of recent on the Stalking Directory forum over here in the UK . The question usually arising after f/l resized fired formed brass won't chamber . I think the question is becoming more regular as more people seem to be trying to just push the shoulder back a couple of thou" .

So here's my and other people on the SD's understanding .

A full length sizing die sizes in the following order , outside neck diameter, body/web , shoulder then finally inside neck diameter . The lengthening occurs when the body has started to be size before the shoulder engages the die, think squeezing a ball or balloon , it gets thinner but longer . Now anyone who thinks the body doesn't get sized would be mistaken , if that were the case no one would ever encounter a stuck case due to lack of lube .

To give some weight to this , I stumbled on this after a rebarrel and purchase of new Hornady dies . I use Redding competition shellholders , they're easy to setup, give consistent results and I'm a bit lazy.

I started with the 0.010 " shellholder and the cases became difficult to chamber and measurement with the comparator saw an increase in length of about 0.002" . The 0.008" saw no measurable difference and chambered fine . The 0.006" resulted in a shoulder setback of 0.001-0.002" shoulder set back , which was my target . These figures are from memory as I didn't think I'd ever need them . I should have perhaps taken note of the effect on the case length by measuring head to neck .



I should add that I had been made aware of this but wasn't looking for it , I was just setting up a die and spring back was unlikely as I anneal .

This isn't an attempt to teach others to suck eggs , more a question of other people's thoughts and observations?

Regards all

So not when the expander is coming back through?

Originally Posted by charliehorse

So not when the expander is coming back through?

No , but I experienced that when I first started using an ultrasonic cleaner , I was obsessed with clean cases . A lack of neck lubrication was causing the expander to drag through the very clean , dry neck . The sizing was fine once the expander was removed and after refitting and lubricating the inside of the necks the problem was solved .

I now only do the minimum of case cleaning , that's only to keep dirt out of my dies and aid case inspection.

That was about 10 years ago and I'm not afraid to say I'm still learning .

Anneal every time and throw away the expander. Heresy. Of course but it works wonders for all the calibres I do. LOL.

Perhaps I have misunderstood the opening statements around the problem, but if a full length resized case won’t chamber as stated, then in my opinion it just hasn’t been sized enough. I’m not sure about the relationship between this problem statement and the following explanation about case lengthening?
If brass lengthens, as you explain, then it is longer at the neck, not longer at the shoulder where it contacts the chamber, so it would not inhibit chambering.
I believe there is more correlation than causation here and one does not effect the other.

Originally Posted by -BW-

Perhaps I have misunderstood the opening statements around the problem, but if a full length resized case won’t chamber as stated, then in my opinion it just hasn’t been sized enough. I’m not sure about the relationship between this problem statement and the following explanation about case lengthening?
If brass lengthens, as you explain, then it is longer at the neck, not longer at the shoulder where it contacts the chamber, so it would not inhibit chambering.
I believe there is more correlation than causation here and one does not effect the other.

I may have poorly explained this , as I said it's come up a few times of recent on the SD forum over here and opinion seems consistent on the cause. On occasion it has been the die being out of spec ' , perhaps the shellholder or just simply the die wound out and in need of adjustment.

I get where you're coming from , had I just f/l sized then I would expect the brass to move into the neck . At the time it didn't occur to me to measure case length to the neck , it would have been possibly of little use but more a point of interest.
This phenomena appears to occur at a point just before the case shoulder engages the die during sizing , which had the die been in contact would prevent the shoulder moving forward .

I can assure you that there is a point at which this occurs , I've measured it using digital calipers and a comparator to measure before and after and I always size 3 or 4 cases during set up first . None of the unsized brass I tried , were difficult to chamber.

It hasn't ever caused me a problem , I just use the appropriate shellholder or previously, just adjusted the die .

I'm sure this can't just occur in the UK .

I guess I just don’t understand the question and I’m looking at end effect from a different angle.

I couldn't disagree more with the original post. In the final stages of a FL die operating the shoulder is being pushed back and the body of the case squeezed. It is not like a balloon being squeezed where the air poops out the top. Brass is a metal it doesn't miraculously flow out the top and lengthen the case. If a case doesn't chamber after sizing it is either too big in the body, too long at the shoulder, too long overall or with belted case types too fat in front of the belt. Or you could have an out of spec chamber. If you are hunting screw the die down to get a solid bump on the shell holder before inserting a case. If you are loading for competition well, I don't need to tell you anything really.

All of these issues can be identified and correct by doing the appropriate measurement.

Originally Posted by -BW-

Perhaps I have misunderstood the opening statements around the problem, but if a full length resized case won’t chamber as stated, then in my opinion it just hasn’t been sized enough.

I don't really agree with this BW. The case may well have been sized correctly, but during that process, brass flowed into the neck causing that to get longer. The shoulder and other case dimensions may well all be within spec.

Couple of suggestions from my side:

If you want to measure sizing in relation to the shoulder (i.e. bump), use the correct size bump gauge to measure the datum line.

To see if you need to trim, measure overall case length AFTER resizing. (@Dermastor) If you don't think cases stretch during resizing, simply measure the case BEFORE and again AFTER. DO multiple measurements, and make sure the flat part of the vernier blade is seated well in the case.

Add to this that when you start using expander buttons in sizing dies things get even more complex.

I don't like expanders at all. For shoulder bumping I either buy body dies, or make them by reaming out the neck on a FL die. And confirm that the die does not touch the neck at all with measurements after sizing.

Originally Posted by ebf

All of these issues can be identified and correct by doing the appropriate measurement.



I don't really agree with this BW. The case may well have been sized correctly, but during that process, brass flowed into the neck causing that to get longer. The shoulder and other case dimensions may well all be within spec.

Couple of suggestions from my side:

If you want to measure sizing in relation to the shoulder (i.e. bump), use the correct size bump gauge to measure the datum line.

To see if you need to trim, measure overall case length AFTER resizing. (@Dermastor) If you don't think cases stretch during resizing, simply measure the case BEFORE and again AFTER. DO multiple measurements, and make sure the flat part of the vernier blade is seated well in the case.

I wasn't disagreeing that cases can stretch, we all know they do. I was meaning that if a case won't chamber, the shoulder hasn't been sized enough. Cases don't datum on the neck, they headspace on the shoulder, a neck can be a fraction too long and does not prevent chambering. If the shoulder dimension is 'in spec' with the chamber it will fit in chamber, it its not 'in spec' it won't fit in the chamber, regardless of the neck. I thought this was fact as far as case an chamber specifications go.
Only in an extreme case that a neck is excessively long it may prevent chambering, but we weren't talking about extreme excess.

Originally Posted by -BW-

I wasn't disagreeing that cases can stretch, we all know they do. I was meaning that if a case won't chamber, the shoulder hasn't been sized enough. Cases don't datum on the neck, they headspace on the shoulder, a neck can be a fraction too long and does not prevent chambering. If the shoulder dimension is 'in spec' with the chamber it will fit in chamber, it its not 'in spec' it won't fit in the chamber, regardless of the neck. I thought this was fact as far as case an chamber specifications go.
Only in an extreme case that a neck is excessively long it may prevent chambering, but we weren't talking about extreme excess.

Ok, so here is an experiment for you.

Get a shoulder bump / body die that is correctly set up. After firing, size your case, but DO NOT trim it. Keep doing this for several iterations. At some point your case will not chamber. The reason for this has nothing to do with the shoulder (you are sizing that and the base of the case body every time remember).

I think there are number of different questions and angles coming forth in this discussion, so I'm just going to clarify what I understand, as we may be talking about different things.

1. Repeated firings and sizings causes brass to 'stretch' or 'flow', requiring trimming of the cases. I think this is established fact and not in dispute.
2. Do cases 'stretch' or 'do the necks get longer' when the shoulder is pushed back during sizing? This I am unsure about. I haven't seen any fact to support this idea, and admittedly have not tried it myself as my measuring devices are not accurate to 3 decimal places, which is what I think the measurement could be if true. Brass is soft, and it seems likely that compressing brass during sizing of the shoulder and body would also bring the neck down with it. So I'm inclined to think that it is not true that necks can grow during sizing. So this is up for debate.
3. Cases chamber/headspace on the shoulder. A slightly long neck should don't prevent chamber if the shoulder has been sized correctly. I don't understand the argument that after sizing a shoulder correctly and within spec a case could not chamber. If it has been sized within spec of the chamber, it will fit inside. Perhaps this is or is not what the OP means, but it seems indisputable to me.
4. Sizing can happen 2 ways, full length, or neck only. The terminology of 'bump sizing' is somewhat misleading, as it is nothing more than full length sizing but only just enough to bring the shoulder within spec of the rifles chamber, but not all the way down to the shellholder. It seems some people do this with or without the expander ball fitted. Correct me if I'm wrong here but this is as I understand it.

Originally Posted by ebf

Ok, so here is an experiment for you.

Get a shoulder bump / body die that is correctly set up. After firing, size your case, but DO NOT trim it. Keep doing this for several iterations. At some point your case will not chamber. The reason for this has nothing to do with the shoulder (you are sizing that and the base of the case body every time remember).

Not quite sure I understand. Are you saying to size the case multiple times?
I'm not sure how that's possible unless you pushing the shoulder back a little further each time, and end up going shorter than that the chamber. Is this what you mean?
Once its sized correctly the first time, then no matter how many times you push the brass into the same die, nothing should change.

Size, fire, size, fire, size, fire...

Think of it this way:

If you measure the case and the shoulder datum is correct, but the case wont chamber, then something else is out of spec, right ? That is why I am saying measure both the shoulder datum and the overall length to figure out what the issue is. It could also be a base issue.. some chamberng, especially target rifles are tight in that area. then you need to use a small base die...

There are a variety of reasons and dimensions why a case may not chamber. The shoulder measurement is only one of them...