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

I'm not going to measure again though in the future other than to set the dies up initially. Kinds of a one time thing while investigating those inconsistent numbers reported in the first post.

Also, am I using the wrong terminology to refer to the case's head-to-shoulder-datum measurement? Or is it in fact called "case headspace"? Someone is sharpshooting me on another forum where I've posted this, with regards to my terminology (without suggesting the correct terminology), but I've looked up the terms for various case dimensions and "headspace" seems to be correct.

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Originally Posted by twadsw01

However, case gauge wouldn't give me actual numbers, right?

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Who needs actual numbers? I've literally NEVER calculated a shoulder bump. I use the case gauge for all 223 since it's mostly autoloader ammo that needs to be sized to SAAMI. And I use the actual chambers on .308 and 300 WM bolt gun ammo.

Having a nominal bump is worthless info to me other than for pretentious coffee shop conversation. ;)

What is the range on the headspace measurement? I'm having trouble finding this information anywhere.

Edit: meaning, the in-spec range. SAAMI or whatever.

It’s a ‘relative headspace’ measure, when using that Stoney Point or Hornady tool. Measuring once-fired brass
from your gun relative to the die setup measurement. Listen to MarkM, he knows what he speaks!

FWIW I use the RCBS ‘X’ dies to limit case neck growth on semi-autos. Larry Gibson (Cast Boolits) got up to 18 reloads per case out of 308s shot out of an M1A (notoriously hard on brass) ... before he gave up, whereas he only got a few reloads before, regardless of how his sizing dies were adjusted.

Why is it "relative"? The SAAMI diagram I found defines the headspace as the length between the shoulder datum (0.330" diameter) and the case head. The collar of the Hornady tool bottoms out exactly on the 0.330" datum point, and you zero your mic at the same point. So, the resultant dimension being mic'd with the Hornady tool is exactly the same dimension as specified in the SAAMI drawing, namely, shoulder datum to case head.

Right?

Quote:

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Originally Posted by twadsw01

What is the range on the headspace measurement? I'm having trouble finding this information anywhere.

Edit: meaning, the in-spec range. SAAMI or whatever.

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There's a min/max on the case gauge. Not sure what the range is, but I'd guess +/- .003-.005"

The case guage is brilliant and honest. Years ago I ran a handfull of rounds that weren't bumped back quite enough to spec correctly in the gauge, and they gave me problems going into battery. A pain in the butt lesson to obey the gauge.

Gotcha. Thanks, man.

I think I understand the case gauge now, and why it isn't giving true headspace, but rather just a measurement of the effect of the sizing die on the case.

I'm setting shoulders back 3/1000" on average, so I think this is acceptable for the purposes of this ammo.

If the cartridge headspace varies as much for my ammo as it does, and I drop it in a gauge, it is going to be all over the place. I've read that those gauges have like a 0.003" range between the short and long cartridge headspace lengths....true??

Quote:

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Originally Posted by twadsw01

Why is it "relative"? The SAAMI diagram I found defines the headspace as the length between the shoulder datum (0.330" diameter) and the case head. The collar of the Hornady tool bottoms out exactly on the 0.330" datum point, and you zero your mic at the same point. So, the resultant dimension being mic'd with the Hornady tool is exactly the same dimension as specified in the SAAMI drawing, namely, shoulder datum to case head.

Right?

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This should be the case but it isn't. The Hornady tool can be used as a comparator only. Meaning you can measure to compare one case to another, or measure a case to compare it to a headspace gauge.
If you measure headspace gauges you will find that there is a big discrepancy, they don't measure what they are. I think the Hornady tool has a chamfer that makes it not measure the true datum line.


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Quote:

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Originally Posted by twadsw01

If the cartridge headspace varies as much for my ammo as it does, and I drop it in a gauge, it is going to be all over the place. I've read that those gauges have like a 0.003" range between the short and long cartridge headspace lengths....true??

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.003" sounds about right. I don't have mine in front of me.

Using a case gauge is fine for hoser ammo, you are just verifying that is will chamber.
It is much harder to eyeball a case gauge for consistency than it is to measure with a comparator.

If you are loading for accuracy, you will want to use your Hornday comparator to make sure you are getting a consistent set back. Something about consistency equaling accuracy.

If you want to "calibrate" your comparator, get a Go gauge and measure it with the comparator. IIRC, the Go gauge is the min headspace for the AR.

For increased accuracy, remove the expander ball (even on Forster dies) and use an expanding mandrel. Neck tension is the key.
You don't really need to crimp the neck. If you do, just remember that your are increasing chamber pressure and pay strict attention if you are operating near the upper limit of that powder. (MK262 clones)

For semi-autos, you want to full length size. Period.

Mixed headstamps can/will give you mixed headspace lengths. Fine for hoser ammo but not precision stuff. Remember that whole consistency equals accuracy thing.

If you want to load precsion ammo, go right to the Forster press. I no longer use my RCBS now.
I get less than .001 difference in headspace on my Forster with my 308 brass.

Yes, you can load precision ammo on a progressive press but it take some/alot of modification and knowing what you are doing.


I can't wait until you discover case and bullet runout.