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Old August 11, 2019, 16:04   #1
Datchew
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an alternate approach to headspace measurement

While learning about reloading and causes of incipient case separation due to undersized base-shoulder brass mixed with oversized headspace, I came up with an idea that might be of use to others who overthink things WAY too much like me.


I used a RCBS precision mic and several pieces of Lake City brass to make resized cases in .001" intervals from 1.625 to 1.635.
I used LC because it's one of the hardest to resize and thus should hold size better than a softer brand.

Removing the EJECTOR from the bolt, you can work through the various cases and find out what your actual headspace is without removing the locking shoulder.

This is an alternative to pulling the locking shoulder and inserting go/no-go gauges and pins.

Hope it helps.

Last edited by Datchew; August 12, 2019 at 15:25. Reason: because an ejector is not a firing pin.
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Old August 11, 2019, 16:15   #2
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On the flip side, I screwed up after loading about 50 or so rounds when the sizing die backed off a tad and was too long a couple of thou. Took the firing pin out and ran them through the chamber to bump the shoulder back on one of my tight HS rifle. It's interesting to take factory cartridges and measure the dimension. Seems most of them are right at 1.630
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Last edited by meltblown; August 11, 2019 at 16:22.
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Old August 11, 2019, 17:52   #3
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By my measurements, most factory .308 Winchester and 7.62x51 measured 0.002” shorter than my Forster 1.630” headspace gage when measured in the RCBS Precision Mic about 10 years ago.

If you make improvised gages with spent cases, keep your Precision Mic nearby to keep track of your “calibration” on those cases. Sized cases deform under little effort when forced into rifle chambers.
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Old August 11, 2019, 18:08   #4
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Quote:
Originally Posted by Datchew View Post
This is an alternative to pulling the locking shoulder and inserting go/no-go gauges and pins.
There is no need to pull the locking shoulder to check the headspace on an assembled rifle, and I see no reason to make short cuts with something explosive you plan to hold up beside your face if starting from scratch. I would not do it with brass cases for love or money myself. YMMV.
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Old August 11, 2019, 20:38   #5
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Why would anyone remove a LS to use pins to check HS when all they need to do is verify it's good with gauges? As long as it's good WGAF what the number is?
I don't get this idea at all.
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Old August 11, 2019, 20:51   #6
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Quote:
Originally Posted by hkshooter View Post
Why would anyone remove a LS to use pins to check HS when all they need to do is verify it's good with gauges? As long as it's good WGAF what the number is?
I don't get this idea at all.
He wasn't quite exact on what he said. But I get it. You really want to know what the headspace is, fire form it with the gas cut off and measure.
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Old August 12, 2019, 05:45   #7
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Better to use a HS gauge and shim stock....
But bench rest and target rifles are routinely chambered using a dummy cartridge, not a HS gauge....
You just need to go easy and feel contact,,,,,none of that slaming it closed or '2 thumbs pressure' hogwash.
No matter what you use, its used as a GAUGE and should be handled and used lightly, like a micrometer or fine watch.
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Old August 12, 2019, 12:55   #8
Datchew
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Quote:
Originally Posted by hkshooter View Post
Why would anyone remove a LS to use pins to check HS when all they need to do is verify it's good with gauges? As long as it's good WGAF what the number is?
I don't get this idea at all.
Ya, I messed up my description.
My reference to the pins was that if you want exact headspace, my understanding is you'd have to pull the shoulder and go through the pins and do basic math.
Or as was mentioned, measure a fireformed case - but I don't have experience there and with brass expanding/contracting, i'm skeptical of that method until I try it a few times. Still... lotsa people have proved it out.

If you're happy knowing it's one of 2 binary choices - in/out of spec - great.

For me, I adjusted all my rifles to 1.632" headspace per the GB book and i'm trying to size my reloads to .003-.004" below that so i can have reliability but also longer brass life.

Man... some of you (not you HKshooter) are passionate about just bouncing ideas around.
Love or money indeed... just go do your thing man. Deep breath.
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Old August 12, 2019, 13:38   #9
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Quote:
Originally Posted by Datchew View Post
I used a RCBS precision mic and several pieces of Lake City brass to make resized cases in .001" intervals from 1.625 to 1.635.
I used LC because it's one of the hardest to resize and thus should hold size better than a softer brand.
You know, they make headspace gauges in .001" increments for those who are interested in doing what you are doing. And they are made of steel, which "should hold size better" than ANY form of brass.

Quote:
Removing the firing pin from the bolt, you can work through the various cases and find out what your actual headspace is without removing the locking shoulder.
Huh? Did you mean extractor? Firing pin is irrelevant. Unless you're using live ammo and not just a resized deprimed case (something only fools do). Locking shoulder removal already mentioned above.

Quote:
Hope it helps.
Helps people learn what NOT to do - yes.

I'm not saying I've never used a known-good cartridge case as a field expedient method of checking headspace. But I've never pretended it was anything more than to determine if something was way over or way under. It is not useful for obtaining any precision measurement. And they actual mean something. Although you'd also need to quantify closing force more than "double thumb".

Which is an interesting thing about the FAL. All the comblock tech data says "close with x kg pressure" does not close with y kg pressure (and it's different in same caliber depending on weapon's locking mechanism). Only the FAL has this arbitrary "double thumb" thing. And that's only in the Commonwealth literature. No mention at all in FN.

You seem to be a passionate reloader and have invested some good money in good equipment. Why not buy a set of gauges made for this? They last a lifetime.
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Last edited by gunplumber; August 12, 2019 at 13:47.
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Old August 12, 2019, 15:20   #10
Datchew
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Doh!

Yes, I meant extractor. I'll go correct it.

I agree - steel is better.
I would speculate these will last exactly as long as it takes to deform one.
But i can measure them before and after if i'm worried about that with the rcbs mic.
Anyway, this is a homebrew (cheap) exercise while i'm having fun learning. At $20-30/pc for steel, i'll stay on these until i get more serious or go pro (neither is likely.) I doubt i'll build or work on more than 5-10 FAL's in my lifetime.

I was thinking about your blurb on double thumb pressure.
Engineering processes use the word "sufficiently"
Lawyers use the word "reasonable"

In my experience these vague terms usually mean:
A - they don't know
B - too lazy to be precise and/or left themselves an easy way out
C - it's not critical
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