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headspace gauge clarification.....

This is a discussion on headspace gauge clarification..... within the Gunsmithing forums, part of the M14 M1A Forum category; I've seen and am hearing that on the 308Win, Forster has a set NO GO gauge length of 1.634. Clymer and PTG have that NO ...

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Old December 16th, 2016, 04:43 AM   #1
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headspace gauge clarification.....

I've seen and am hearing that on the 308Win, Forster has a set NO GO gauge length of 1.634.

Clymer and PTG have that NO GO set at 1.636.

If I have a set of Forster gauges, should I just use the 1.636 as the NO GO gauge, or remain at the original NO GO gauge length of 1.634. OR, should I just standardize the system of the NO GO being 1.636?

I know the 308 vs 7.62 NATO differences in gauge lengths, but why companies have different set standards for 308 is a little baffling to me. Looks like it should be standardized..

My question is.... which is it?

I'm setting headspace on a couple of builds, and want them to come in at 1.632/1.633.

Just want clarification as to what to look for on NO GO length and what set standard I should use. Thanks!!

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Old December 16th, 2016, 05:17 AM   #2
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If you haven't seen it, all your answers should lie here...

A little bit of everything to do with headspace.

Personally, I like to set my builds to 1.632" to 1.634" when new.

Here are the official guidelines as per Gus Fisher...

Headspace lengths for caliber .308 Winchester

1.630" GO
1.634" NO GO

The G.I. Headspace Gage lengths for 7.62mm

Go Gage...................................... 1.6355"
NO Go Gage................................ 1.6375"
Rebuild Maximum Gage.............. 1.6415"
Field Reject Gage....................... 1.6455"

I wouldn't build anything over 1.637". If you hit 1.638", then it's time for a different barrel or a Bula armorer's bolt.


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Old December 16th, 2016, 06:37 AM   #3
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I didn't know about the post from Gus! Thanks Tony. Awesome information!

One question i still have.. Should we today, consider that 1.634 is the NO GO standard length for 308, or should we use the "New Common length" at 1.636?

Like you, i'm shooting for my hs to be 1.632.. 1.633 at the most.

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Old December 16th, 2016, 06:59 AM   #4
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My understanding is that the NO GO gage is primarily a Quality Control test for the installer of the barrel - and that the dimension of that gage depends on how much leeway from the GO gage minimum of 1.630 the installer feels is acceptable.

The HS of the install should be partially based on what ammo and what conditions the end-user chooses. For most dependable chambering of 'unknown ammo' and in heavily fouled chambers, a large chamber HS would work.

If you want to verify that your installations do not HS more than 1.634, then use that gage. If your HS goal is some precise number between 1.630 and 1.63x, then you'll need a reliable way to measure the actual HS.

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Old December 17th, 2016, 03:35 PM   #5
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Actually... the no go gage is used by the military to establish the limit for rifles to be deployed outside of the CONUS. Riffles with head space of 1.636 (this is a newer standard as the old was 1.638) or longer are not to be deployed. They may however be used for training and are considered serviceable with head space up to 1.6415. hope that didn't bust anybody's bubble. The new tighter standard was established because most 7.62mm rifles in use today are for DMR, SDM, and sniper use.

That said, It's my policy to build rifles with head space between 1.631 and 1.634 which generally shoot about any ammo pretty good.

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