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

[P2000]

Under the wrong conditions, full length sizing can make headspace longer. And firing can make the headspace shrink. This is a sign that you are not bumping the shoulder back enough.
I have no good explanation as to how headspace is changing during seating/charging.

Sent from my XT1565 using Tapatalk

[twadsw01]

Thanks, P. I'm going to make it out to the range this week, and I will obtain some freshly-fired brass and measure that too.

I may even proceed to resize some of it, just to see what a given piece of brass does on the way through my process, to confirm that the observations posted above are indeed consistent.

[markm]

Expander balls ripping out of your case on the upstroke might be the problem. I run a die without the expander ball, and use a neck expander die which sizes on the down stroke.

If you must run the expander, lubing the inside of the necks will help reduce the havoc those things do to your brass.

[markm]

And.. get a chamber gauge. Good God that's a lot of wasted time measuring head space.

[twadsw01]

Thanks, Mark.

How much faster is a case gauge versus putting the case between two jaws of a mic with a Hornady headspace gauge clamped on?

Could FL size/decap without the expander ball, then try one of those neck sizers. Any downside to this approach? Is neck lube still required?

And.. get a chamber gauge. Good God that's a lot of wasted time measuring head space.

[twadsw01]

Ah, you're saying for this particular set if observations. Gotcha.

And.. get a chamber gauge. Good God that's a lot of wasted time measuring head space.

[markm]

Thanks, Mark.

How much faster is a case gauge versus putting the case between two jaws of a mic with a Hornady headspace gauge clamped on?

Could FL size/decap without the expander ball, then try one of those neck sizers. Any downside to this approach? Is neck lube still required?

I don't use neck lube. The only downside is you have two steps instead of one. Depending on how good you want the ammo to be, it may be worth it. Also... the upside to the neck expander die is that you have almost no case trimming to deal with on reloaded brass because the case stretch is eliminated.

Once fired XM193 brass for example will still require massive trimming. But subsequent loads will require very little trimming.

[dmd08]

I don't use neck lube. The only downside is you have two steps instead of one. Depending on how good you want the ammo to be, it may be worth it. Also... the upside to the neck expander die is that you have almost no case trimming to deal with on reloaded brass because the case stretch is eliminated.

Once fired XM193 brass for example will still require massive trimming. But subsequent loads will require very little trimming.

Mark, what neck sizing die do you use?

[twadsw01]

No problem on a progressive, to have two steps versus one, that is. May try that.

Thanks, man.

I'm also going to track the headspace of a case all the way through the reloading process.

I don't use neck lube. The only downside is you have two steps instead of one. Depending on how good you want the ammo to be, it may be worth it. Also... the upside to the neck expander die is that you have almost no case trimming to deal with on reloaded brass because the case stretch is eliminated.

Once fired XM193 brass for example will still require massive trimming. But subsequent loads will require very little trimming.