case length and neck tension consistency

[solst_ice]

Hi guys,

I've got a problem with inconsistent neck tension and case length. I got 300 new .308 Lapua cases last year and prepared them before the 1st firing:

- did a FL calibration using a Redding standard FL die
- trimmed the cases to 2.005"


After that, I did some load development ( used different amount of powder charge in a batch of 5 respectively ). After the 1st firing, I measured the case lengths. I got values between 1.998 - 2.002 . I don't know why they varied that much, maybe because of the different pressure caused by different powder charges. Right now, they have been fired 3 times, but the length did not change much again after all. Means, the case lengths are pretty inconsistent right now. Maybe it would have been a better idea, to do the trimming after the 1st firing?

Some questions:

1) How do you get and keep consistent case length with new brass?

2) What would be the right way for me to get consistent case lengths right now? Just shorten them all to the shortest length (1.998)?

3) Is there any way to avoid unbalanced case lengths between different loading charges?



After the 1st firing, I'm only neck sizing the brass. I use a Redding competition neck sizing die equipped with a .336 bushing.
When I started reloading, I was told by my mate, that it would be better for consistency just to size 1/3 of the neck. That's what I'm still doing today.

Now the issue I got with the neck tension:
I've recognized, whenever I'm seating a bullet with a Redding competition seating die, that the amount of force needed to push the bullet into the case varies. Sometimes there no force at all needed, sometimes it takes a lot of pressure. I was just wondering, how that is possible.


4) Could have different case lengths an influence on the neck tension also? (should affect the length of the bearing surface between neck - bullet)

5) If so, would it be advisable to size a greater portion of the neck than just 1/3?

6) Would it be advisable to use a tighter bushing and a mandrel to open the case neck up a bit afterwards? Or to use a Lee Neck Sizing Collet Die?



Thanks a lot for your tips.

 

[Deleted member 10043]

You are going to get different case lengths. I only trim when cases start to become too long. Find a SAAMI schematic. You will see a min/max for case length. Don't sweat the small stuff. I do use the Lee collet die until they become too tight in the chamber and then partial FL size. I don't mess with hot rod dies. I use plain vanilla. Another trick is to chuck a bore brush with case lube and run it down the neck before sizing.

 

[TripleBull]

What would be the right way for me to get consistent case lengths right now? Just shorten them all to the shortest length (1.998)?

If you ran them through the FLSD again, typically you'd see they have grown back, possibly longer than your earlier 2.005". You'll have a limited number of firings using only a neck bushing die before case diameter will make them tight in the chamber, possibly too tight to chamber.

Would it be advisable to use a tighter bushing and a mandrel to open the case neck up a bit afterwards? Or to use a Lee Neck Sizing Collet Die?

I don't know if you need a tighter bushing or not. Decide on a neck tension target spec and go from there. You don't want to overwork the brass in the neck. Are you annealing? I do like the mandrel approach and do get uniform neck tension that way.

 

[whatsupdoc]

Couple of things, I never trim new brass only chamfer inside of the neck. Once it has been fired I check the length after resizing.
Eventually you will have to full length resize your brass because it will be to tight for the chamber, so why not do it all the time and be consistent.
Dont know anyone who resizes 1/3 of the neck.

Full length resize the cases bumping the shoulder back .001 to .002 get a mandrel die and expand the neck then trim the cases.

 

[spife7980]

1) How do you get and keep consistent case length with new brass?
You generally dont unless the brass is prohibitively long. After firing it once to expand towards chamber dimensions less spring back and the full length sizing should make the body equal. You can then trim off the inconsistencies that result after that process.

2) What would be the right way for me to get consistent case lengths right now? Just shorten them all to the shortest length (1.998)?
Full length size the cases for .002" of shoulder set back to uniform their outside dimensions and then trim. Depending on the dimensions of the brass that iece thats shortest could end up longest once run through a full length die. You have to remember on that first firing its not only growing in length, its growing radially to fill the chambers diameter. Some may have been skinnier which means that it expands more than the others which then further means that some of that neck brass will get pulled back into the body. Without qualifying its diameter differences we cant say why that one ended up shortest.

3) Is there any way to avoid unbalanced case lengths between different loading charges?
Not really. Full length sizing should help make all brass more uniform from one to the next. Once the body dimensions are uniformed from full length then you can trim the ends off to make that uniform.

4) Could have different case lengths an influence on the neck tension also? (should affect the length of the bearing surface between neck - bullet)
Yes but its a negligible amount if we keep the case growth to reasonable expectations, a thousandth or two here or there wont make a big difference. Letting the brass grow a couple firings shouldnt effect the total amount of neck tension all that much.

5) If so, would it be advisable to size a greater portion of the neck than just 1/3?
Yes, size the whole neck.

6) Would it be advisable to use a tighter bushing and a mandrel to open the case neck up a bit afterwards? Or to use a Lee Neck Sizing Collet Die?
Cant say because you dont give us the loaded round diameter from which to calculate your bushing size, only that you are using a .336. Generally you want the bushing to size .003-.004 under loaded round diameter and then open up to .002" with the mandrel. By your phrasing your .336 is probably .002 under the loaded diameter and you arent using any expansion step but thats just assumption.

 

[solst_ice]

Hi guys,

really great information! Thanks a lot!!
Now it seems to me that FL sizing with 0.001 - 0.002 of shoulder after every shot leaves the cases much more consistent than neck-sizing only what I've done so far, right?

I've never bumped the shoulder back till now. Is there a special die for that? Or should I just use the Redding Competition shellholders in the right size and the normal Reding FL die / TYpe S die?

Unfortunately, I don't have a Type S FL die so far, only the Standard Redding FL die and the competition die set. But from my current point of view the competition dies are pretty useless but the seating die. For the FL and neck sizing it would take 2 steps instead of one if I would like to use the bushing for neck sizing.

The neck diameter with a seated bullet is .337 . Means, I would have to use a .333 - .334 bushing for the .002" mandrel?

 

[spife7980]

To bump the shoulders back you just need a regular full length die, thats basically all I use. A full length bushing will minimize the overworking of the neck material but other than that aspect it does the same exact thing as a standard full length die does.

You can achieve the bumping of your shoulder with the redding shell holders or you can just adjust the die in its lock ring if you dont feel like buying a set of 5 shell holders. I use the hornady headspace comparators and adjust to where the length is .002 less than fired. But if youve already bought or dont mind paying for them the redding comp shell holders should make it easy to adjust quickly.

Before buying any more dies and shell holders I would just try it with the full length die you already have. Size a piece without the expander ball to measure how small it sizes it down to. Then do it with the expander ball installed and you can see how much it opens it back up and what your resulting tension/interference fit is of a loaded round.

Once you know what you have and where youre at youll be better able to see where you need to go as far as bushing dies and mandrels go.

 

[solst_ice]

To bump the shoulders back you just need a regular full length die, thats basically all I use. A full length bushing will minimize the overworking of the neck material but other than that aspect it does the same exact thing as a standard full length die does.

You can achieve the bumping of your shoulder with the redding shell holders or you can just adjust the die in its lock ring if you dont feel like buying a set of 5 shell holders. I use the hornady headspace comparators and adjust to where the length is .002 less than fired. But if youve already bought or dont mind paying for them the redding comp shell holders should make it easy to adjust quickly.
View attachment 6902032

Before buying any more dies and shell holders I would just try it with the full length die you already have. Size a piece without the expander ball to measure how small it sizes it down to. Then do it with the expander ball installed and you can see how much it opens it back up and what your resulting tension/interference fit is of a loaded round.

Once you know what you have and where youre at youll be better able to see where you need to go as far as bushing dies and mandrels go.

Sounds good. I will try that. Thanks a lot!

 

[solst_ice]

Btw, I'm not annealing so far. But according some opinions on SHide it's worth to do it to keep neck tension consistent and to increase neck live.
What do you think about it?

 

[spife7980]

I do it but thats something you can worry about down the road, you have bigger bridges to cross first. Its one of those last 5% things, worry about the first 95% for now.