Nonsensical Headspace Measurements on 223rem cases...??

[twadsw01]

How would full-length sizing a case increase the headspace measurement on a .223 case, and charging/seating/crimping decrease the headspace measurement??

This weekend, I started taking headspace measurements on some 223 cases in my stockpile in various states on the way to being reloaded, in hopes of starting the process of setting up my new Dillon 650 for reloading 223. I measured unprepped and prepped cases, as well as fully loaded rounds (definitions included below). All of the work done on the cases was performed on a Lee Turret press.

The observations which do not make sense to me, are that:

1) the fully loaded rounds have a shorter headspace (length from case head to the "datum" on the cartridge's shoulder, 0.330" diameter) than the prepped cases (cases which have been sized and primed ONLY), and​

2) the prepped cases have - on average - a longer headspace than that of the unprepped cases.​

What is going on??



Data is for headspace dimensions measured for 223 cases in various states in the reloading process.

"Unprepped": picked up of the range, most likely once-fired through my rifle.
Mean = 1.463603"
Median = 1.464"
Std. Dev. = 0.001701"
N = 34

"Prepped": full-length sized, primed, and trimmed to proper case length.
Mean = 1.465595"
Median = 1.468"
Std. Dev. = 0.004535"
N = 21

"Loaded": prepped cases that have been charged with powder, bullet seated, and crimped. In other words, fully loaded rounds, ready to fire.
Mean = 1.456017"
Median = 1.4555"
Std. Dev. = 0.003062"
N = 30

There are uneven numbers of cases in each category because I just grabbed a random number of prepped and unprepped cases from my reloading bins, and there are 30 rounds in the loaded column because I went through and measured what I already had loaded in a magazine.

The uniform dimensions of the unprepped cases I take to be due to the fact that most of them came from my rifle (i.e., they have been expanded to somewhat uniform dimensions by the rifle's chamber itself). Now, some of the cases I picked up at the range were not fired from my rifle, so the outliers in the unprepped case category could be due to that, or at least some of them could be due to that.

Unprepped
1.464
1.464
1.464
1.464
1.4635
1.464
1.465
1.466
1.464
1.461
1.465
1.464
1.462
1.463
1.459
1.4635
1.465
1.464
1.464
1.465
1.46
1.464
1.463
1.46
1.46
1.464
1.464
1.465
1.4645
1.464
1.465
1.465
1.464
1.466

Prepped
1.466
1.4685
1.468
1.466
1.468
1.47
1.466
1.461
1.468
1.455
1.468
1.468
1.467
1.465
1.468
1.469
1.457
1.468
1.459
1.459
1.473

Loaded
1.452
1.458
1.452
1.453
1.4535
1.459
1.462
1.459
1.452
1.456
1.461
1.46
1.456
1.454
1.46
1.455
1.453
1.458
1.452
1.458
1.452
1.454
1.459
1.46
1.455
1.457
1.454
1.453
1.455
1.458

 

[buffybuster]

Cases can grow during the sizing operation if the die does not make contact with the shoulder of the case. Think of this; the case is forced into the die, the sides of the case are sized down the only unsupported area of the case is up. If the case makes contact with shoulder of the die then the only unsupported area of the case is the neck, which is where you see case growth. If your sized cases have longer headspace measurement than your unsized cases that means your die is not making contact with the shoulder of the case.

Your loaded rounds have a shorter measurement because probably during the crimp the case is pushed back a few thousandths which could be the result of inconsistent case length or excessive crimp.

 

[twadsw01]

Thanks, buff.

All of that makes sense. My shell holder bumps up against the sizing die, however, so presumably I've been resizing them to the minimum possible size. Correct? I will double-check this, hopefully/possibly, in the coming week or so; I'd like to get to the bottom of this ASAP, which may involve me going and firing some of my most recent reloads and taking them all the way through the reloading process and measuring at each step.

Now, you bring up an interesting point - if the sizing die isn't making contact at the shoulder, thereby causing the headspace to lengthen during the sizing process (and the overall case length, along with the headspace, correct?), then the inconsistent case length could be causing the crimping step to push the shoulder back a few thousandths. Does that sound plausible?

Oh, I just thought of one more thing that lends credence to your theory: I trim the cases by using a trimmer that indexes off of the case shoulder and trims, chamfers, and deburs all in a single step. So, if the case's headspace is inconsistent, the overall case length will be inconsistent.

 

[Supersubes]

Could you be crimping a bit to much and collapsing the shoulder? Easy enough to narrow it down. Just follow a few through the process and see what step is doing it.
Im going with the crimp.


The growth between fired and sized is caused by what Buffy is describing.

 

[JCCinOhio]

Also if your seating pressure is too high you can 'crush' the shoulder down a bit when seating the bullet. Make sure to do a good chamfer, and reduce neck tension if it's too tight.

 

[buffybuster]

If you're loading on a single stage press you could take a few thousandths off the caseholder (cheapest part). Considering you're using a 650, make sure you've taken up ALL the slop in the press and die toolhead, before you start modding anything. Since you're trimmer indexes off the shoulder that would make your trim length vary as well and as mentioned, put a chamfer on the casemouths.

 

[twadsw01]

Loaded everything I have done so far on a Lee auto-indexing turret press. So, yeah, single stage.

Bullet seating pressure has always been minimal, and I chamfer and deburr each case neck.

Has anyone ever heard of expander balls lengthening the headspace if there is not a proper amount of lube inside the case neck?

 

[NighthawkCG]

I've seen it with mine where the amount of lube can effect the length. There Honestly I forget if it were with .223 or 300blk, but there was a a day I could pretty much call the headspace based on the feel of the case coming back out of the die. I lube my cases a bit better now and seems to get pretty consistent headspace measurements.

Disclaimer: This was sometime ago around my transition from a FL die, to a redding type-s FL bushing die which I tried with and without the ball. I am not sure on which die or configuration I was using at the time, but definitely had it narrowed down to feel/lube coming out of the die.

 

[twadsw01]

So, here is some additional data, which indicates that my initial measurements prompting this thread might have been erroneous in some way (maybe not zeroing out the mic, etc., etc.,?). I took twenty cases from totally unprepped through the reloading process, sans powder and primer. The purpose was to be able to see how individual cases were effected by each step in the process.

The same process as I normally employ for reloading was used, and I did not ensure the inside of the necks were lubricated (simply due to the fact that I wanted an apples-to-apples comparison with the cases I originally measured for this thread).

I will dump the raw numbers (screenshot form), and two box plots, showing length and headspace after each reloading step (where applicable - e.g., did/can not measure case length after a bullet has been seated).

In my opinion, nothing looks out-of-place here. Cases lengthen after sizing then the longer cases are indeed being trimmed while the shorter ones aren't touched by the trimmer - this is readily observed by the box plot, where it appears that simply the top of one box has been lopped off, leaving the bottom untouched. Also, unprepped cases starting with longer headspace get bumped by the sizing die, while shorter headspace cases do not, and none are being bumped back an undue amount, it seems (0.002" on average).

- Average case length comes out to 1.750", as desired.
- Average cartridge headspace is 1.462".
- Average case length growth from the sizing die is ~10/1000".
- As mentioned before, average shoulder setback is 2/1000".

There are still some high outliers in the headspace category, which could be explained by the spring back phenomenon, possibly.

Of note is that the one case that started with shorter headspace than where the sizing die was bumping all the shoulders back to - case 18, 1.461" unprepped headspace measurement - this case's headspace actually became longer in the sizing die, as expected because of the brass growing while being inserted in the die, but the shoulder never being setback by the die. Is this a concern? I.e., could this case the head of the case to become unduly weakened due to the brass never being 'crunched' back down at the end of the stroke?

Does anything look strange, unexpected, concerning about any of this?

Also, thank you, everyone, for all of the input into this thread. I appreciate it.


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[whatsupdoc]

Couple of things.

If your die is not capable of bumping the shoulder back there is no way to get a consistent case base to datum dimension.
(I have a FL .222 die that cannot bump the shoulder back, I use a modified shell holder to overcome this issue.)

Find a long headspaced case and resize it in your die with the press fully loaded, shell holder against the die and then measure it.
Anything shorter will not be touched by the die and if not properly supported by the shoulder of the die the case shoulder will be squeezed forward and will get longer.
The displaced brass has to go somewhere.


Even if you do bump the case shoulder back there will be some variation due to spring back of the brass (annealing before resizing will minimize this).
Different brands of brass will require readjustment of the sizing die to provide similar headspace dimensions.


Crimping using a roll crimp many times will bulge the shoulder.