Where did the case length go?

[MVW]

I took some 223 brass and ran it through a FL die without the expander button and then used a Century 21st expander mandrel to open up the neck. The headspace measurement didn't chnage after expanding, but the case length decreased by ~0.003" to 0.004". I assume that the downward pressure from the mandrel is compressing the case somewhere. Any idea where? Using the expander button doesn't cause that problem.

Thanks, Mike

 

[Lapua40X]

How deep did you run the expander button? Did the case contact the upper portion of the die?
Don't understand what you mean by "wobble". Is that perhaps your experience when checking them for run-out after steel wool polishing? If that's the case, you may not be getting them into the FL sizing die perfectly straight (dirty shell holder, shell holder misaligned, etc.) or a similar oversight when neck resizing with the expander die.
Are you allowing the expander mandrel to float or are your tightening in the die enough to prevent floating?

 

[MVW]

The mandrel does float and I am not hitting the top of the case. O-ring under die and o-ring holds shell holder on press.

When I use the expander button in the die I don't get the case shortening, so I am wondering what is different.

 

[Clod-NC]

Hi MV,Hi all

MV,considering your description of how you use your FL die without the depriming rod(and expander mandrel,because that's also what it actually is),I reckon your problem is:your cases get overdone by the neck portion of the FL die,then when you come to your next step of expanding with the 21st Century mandrel(mounted in their specialised die just like the one I have),your necks are so tight that the mandrel has to force its way into the neck,thus exerting too much pressure on it,causing the reduction in length...Which doesn't occur with the die's expander mandrel that will resize your neck on the upstroke of the press,thus pulling it back to its original dimension...I suggest you try and acknowledge the actual process of the FL die with and without the depriming rod,first by feel on the press lever,and then on the case neck with your caliper(make sure you measure the neck OD after sizing without the depriming rod,and then with it)...Hope it helps.

 

[MVW]

Clod-NC: I think you are right. The FL die takes the neck down from .25" to .24" - a lot. As you suggest this does create a lot of work for the expander mandrel. What do you think is getting smaller given that the headspace is not getting measurably smaller? I wonder if it is the junction between the neck and the shoulder that is getting distorted.

Mike

 

[Clod-NC]

Mike
I wouldn't know at all,I actually haven't given much thought to it,but using an FL die without the decapping rod made me aware of that extremely reduced neck OD(I was using Hornady FL die on 300WM),that's why I directed you there...Maybe a specialist like Boyd Allen will be able to answer your question;I hope he pops out and explains...It's Xmas so why not?This brass has to go somewhere anyway,so maybe you're right...Good luck with your quest and a merry Xmas to you.

 

[Tozguy]

I am having exactly the same problem. After necking some 223 cases up to 6mm, the case has shortened by .005 to .008". The neck is also crooked. The neck can be straightened out by running the case through a collet die. I sure hope that the case length will grow back to normal after the first firing.
Mike

 

[rocketron]

i don't really know how to write this so someone can understand what i'm trying to say, but i'll try

this is what i see happening. when you increase the id of the neck you are shorting the shoulder length.
it makes the length from case head to the neck shoulder junction shorter. in turn it shortens the case.the more you expand the shorter the case and shoulder gets.

 

[Tozguy]

Good work Rocket, I understand your explanation. Thanks. Mike

 

[Webster]

I don't really know the source of the case getting shorter. Here is my guess. The shoulder is the weak area, it's on an angle. I believe the case is unsupported by the die except when the shell holder is touching the bottom of the die. If the shell holder is any lower then the case sides and shoulder don't contact the die. Only the shell holder is touching the case. The case is tapered. If you FL size and then pull an expander ball from the inside of the case and exit the neck I would think it would pull the shoulder forward (it isn't supported by the die) It is more likely to pull the shoulder forward than stretch the case side walls. If you FL size without an internal sizing ball and push a tapered expander mandrel that's larger than the neck opening it would push the shoulder downward. Your only talking about 0.004". If someone has one of the gauges that measures the overall length based on measuring the case head to a point on the shoulder it might verify this.

I use a Wilson straight line seater why does it take more effort to seat flat base bullets compared to boat tails. FB bullets have a small radius?

 

[jlow]

Clod-NC: I think you are right. The FL die takes the neck down from .25" to .24" - a lot. As you suggest this does create a lot of work for the expander mandrel. What do you think is getting smaller given that the headspace is not getting measurably smaller? I wonder if it is the junction between the neck and the shoulder that is getting distorted.

Mike

My guess is you are right on there and the internal junction where the neck and shoulders meet is now lower by that 0.004" you are missing at the top. The problem with this is despite the fact that the headspace is not changed (that is measured further down the shoulders), if you neck turn your brass and your turner was initially set to just scrape the shoulders, you may no longer be able to reach it - that might in fact be one way to test this idea.

 

[rocketron]

here is a .223 case. left one was sized with a 6mm expander.it lost .003 in length. then expanded to 6.5mm it lost another .006 in length. you can see then neck shoulder junction is lower.

 

[jlow]

Just looking at them, I would say the difference is a lot more than 0.009".

 

[bigedp51]

Any reduction in neck diameter will always cause an increase in length, and any increase in neck diameter will always cause an decrease in length when neck sizing.

A fired case is always shorter than a full length resized case.

You cannot destroy matter, you can only rearrange it.

Example: When the .303 British cartridge case below was fired, the front part of the case was sucked into a black hole. When the case reached the opposite end of the black hole its matter expanded creating another "big bang" and caused the shooters expanding universe. (and the case became shorter)

Moral of story, when firing old surplus ammunition always wait for the click................... and "then" the bang before opening the bolt during a mad minute.

Reference: Whatsamatta U higher Edumacation Department.

Resizing - Case Dimension Changes
by: Germán A. Salazar

http://riflemansjournal.blogspot.com/2010/06/basics-resizing-case-dimension-changes.html