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View Full Version : Head space gauges, NATO?


Groucho
July 07, 2007, 19:49
Where can I pick up a set of NATO spec. head space gauges? Trying to check my M1A. It has a NATO spec barrel (TRW 1963). Bolt will just close on a .308 no-go gauge and I'm told that's OK since it's a NATO chamber. However, I'd like to be certain, if that's possible. Or, am I just being an old worry wart?

Groucho

vmtz
July 07, 2007, 21:37
I got a set of No GO and Field from Clymer (sp).

Vince

shootist87122
July 07, 2007, 22:23
IIRC, there is no such thing as a NATO spec chamber - various members have diff specs with the US having one of the largest dimensions for Field gauge. If shooting NATO spec ammo you should be fine. Brownells sells .308 gauges in increments of .001". I bought a 1.636 and 1.638 (1.638 is SAAMI .308 Field) to use on my Ishapore. I would suggest you get one or both of those.

For reference FN Field spec for the FAL is 1.640.

Groucho
July 08, 2007, 08:17
Originally posted by shootist87122
IIRC, there is no such thing as a NATO spec chamber - various members have diff specs with the US having one of the largest dimensions for Field gauge. If shooting NATO spec ammo you should be fine. Brownells sells .308 gauges in increments of .001". I bought a 1.636 and 1.638 (1.638 is SAAMI .308 Field) to use on my Ishapore. I would suggest you get one or both of those.

For reference FN Field spec for the FAL is 1.640.

OK, getting in over my head here. "Go" and "No Go" I understand. "Field" is getting fuzzy for me. Does this mean it's OK to shoot, but....?

I was also looking for solid numbers based on what appears to be a false assumption that the go and no-go lengths for NATO spec. were set. Yikes, I think I've opened a can of worms.

Thanks for your help.

Groucho

shootist87122
July 08, 2007, 08:38
Field is the Failure measurement (absolutely unsafe to shoot). US commercial SAAMI FIELD is 1.638. FN FIELD spec is 1.640". US military for the M14 (using military ammo with thick brass of course) is even bigger. Clymer and Forrester will be SAAMI spec unless specifically marked otherwise.

SAAMI:

GO 1.630
NOGO 1.634
Field 1.638

FN Specs:

GO 1.6315
NOGO 1.636
Field 1.640

If you are shooting US commercial brass (thinner brass than military brass = more likely to rupture) you need a bit tighter chamber on the high end for safety.

Since you reload, you can custom fit your brass to your chamber, by only partially full length resizing. That should also extend the life of the brass in that rifle.

vmtz
July 08, 2007, 09:00
The ones I have are marked as follows:

Clymer 1203
7.62 NATO
No Go


Clymer 995
7.62 NATO
-Field-

Vince

W.E.G.
July 08, 2007, 09:19
You really should consider obtaining an RCBS Precision Mic.

This will allow you to measure the actual dimension of your gages, and any ammunition in that caliber. Then you can eliminate any confusion from what "some guy on the internet" said.

http://www.centerfirecentral.com/productreviews/precisionmic.htm

Groucho
July 08, 2007, 18:02
As usual, good information on this forum. Thanks so much. I'll be picking up some gauges probably in the length of FAL types since we're talking a "standard NATO spec" (yeah right).

Groucho

Radio
July 08, 2007, 20:49
I use the Forster GO 1.630" and NO-GO 1.634". This is what I use for headspacing. Later I picked up a Clymer NO-GO 1.636" which is my own personal FIELD... when a rifle ever chambers that gauge, it's getting a new locking shoulder.

Either brand will work just fine if you know what sizes you're getting. Most headspace the FAL to 1.632".

"Sizing" the brass by fire forming will work only in that ONE rifle. Every one of my FALs has a slightly different headspace, no two are the same. This difference will still stress your brass, unless you segregate each group of brass to stay with that ONE rifle only... otherwise you might as well mix-n-match.

--Radio

vmtz
July 11, 2007, 09:00
Here is what the GCA has to say about the subject in relation to .308 Garands.

http://www.nmia.com/~daykin/308v762.JPG

Vince

Radio
July 11, 2007, 13:34
If you headspace your rifle using a 1.630" headspace gauge, Forster (probably) or (possibly) Clymer, for a final 1.632" headspace, it doesn't matter whether you shoot NATO or commercial because you have set your rifle to digest BOTH in a safe and reliable manner.

If, on the one hand, you worry and sweat the NATO thing and headspace to such larger dimensions, you will be able to fire NATO rounds safely, but could have problems with thin commercial brass.

If, on the other hand, you ignore the entire tempest and simply headspace your rifle to about 1.632", as has been recommended for many years, you are good to go with ANY ammunition. This is PROVEN with many thousands of rifles over many years and decades.

"A difference which makes no difference is no difference." --Robert Heinlein

--Radio