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  #31  
Old 11-20-2012, 06:44 AM
steelap steelap is offline
 
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Quote:
Originally Posted by rojkoh View Post
For a true 7.62x51 chamber, get the Forsters:

HG762NATOmin and HG762NATOmax gauges. These cover min and max instead of a field gauge.

Reason I do use the Forsters: I can cheat and not strip the bolt.
I just checked my order from Brownell's - and am not happy.

The
319-000-006WB 7.62 Nato Maximum Chamber Gauge Mfr Part: HG762NATOMAX is right.

BUT, the Forster headspace gauge sold as
100-010-714WB 7.62 Go Gauge Mfr Part: HG30816330SP is NOT the HG762NATOmin gauge - it has a length of 1.6330, not 1.6355 as shown for the HG762NATOMin on the Forster website. The gauge itseld is not marked by Forsters as 7.62, but rather as .308/.243.

I am trying to understand why Brownell's would sell an improper gauge (1.6330). Too short for a 7.62 GO (1.6355), too long for a .308 GO (1.630).

Any suggestions on what caliber or purpose to use this headspace gauge?

By the way, neither has the relief cut for the extractor.


Last edited by steelap; 11-20-2012 at 06:50 AM.
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  #32  
Old 11-20-2012, 06:52 AM
steelap steelap is offline
 
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Quote:
Originally Posted by nf1e View Post
I have gotten two sets of guage from CMP both sets are marked 7.62 NATO.
I can't find these on the CMP estore website. Only .308 headspace gauges.

Does CMP no longer sell them?

"Life is Good!"
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  #33  
Old 11-20-2012, 06:58 AM
nf1e nf1e is offline
 
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Location: Connecticut
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I think you will find confusion all over on this subject.
One Nato go is 1.6330 and another Nato match go is 1.6325
The 1.6355 in the Nato match no go.
I try to stay away from forsters. They don't seem to agree with any that I personally use. That's why I decided to just use the CMP guages and be done with it.
Good luck. God knows we all need it.
Semper Fi
Art
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  #34  
Old 11-20-2012, 09:27 AM
hammonje hammonje is offline
 
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Location: Union, KY
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Uh...why not just use 308 Win gauges like the rest of the world and MAKE LIFE EASY.

Unless you are trying to find out if a 7.62 NATO Navy B/R is in spec. I have been able to confirm headspace on every commercially built M14 I own with my Forster gauges so they must be OK. The armorers I know use 308 Win gauges, not 7.62 NATO.

Why do you guys want a 7.62 NATO chamber??????
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  #35  
Old 11-20-2012, 09:42 AM
nf1e nf1e is offline
 
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Location: Connecticut
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Quote:
Originally Posted by steelap View Post
I can't find these on the CMP estore website. Only .308 headspace gauges.

Does CMP no longer sell them?

"Life is Good!"
When you get to estore click on .308 guages and you will see a photo. They are 7.62 Nato.
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  #36  
Old 11-20-2012, 10:54 AM
M14 M14 is offline
 
Join Date: Jul 2011
Location: south mississippi
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Quote:
Originally Posted by steelap View Post
I just checked my order from Brownell's - and am not happy.

The
319-000-006WB 7.62 Nato Maximum Chamber Gauge Mfr Part: HG762NATOMAX is right.

BUT, the Forster headspace gauge sold as
100-010-714WB 7.62 Go Gauge Mfr Part: HG30816330SP is NOT the HG762NATOmin gauge - it has a length of 1.6330, not 1.6355 as shown for the HG762NATOMin on the Forster website. The gauge itseld is not marked by Forsters as 7.62, but rather as .308/.243.

I am trying to understand why Brownell's would sell an improper gauge (1.6330). Too short for a 7.62 GO (1.6355), too long for a .308 GO (1.630).

Any suggestions on what caliber or purpose to use this headspace gauge?

By the way, neither has the relief cut for the extractor.

You can use those gauges to check the headspace on all these calibers.
308,
7mm-08 Rem,
7.62 x 51,
243 Win,
260 Rem,
338 Federal,
358 Win

Your 1.6330 gauge is a perfect headspace by the way. I set all mine like Art at 1.6325, which is only one half thousandths less than your gauge. As I said before, it takes years of practice and many rifles checked, to learn the feel of one half a thousandths in your fingers.

Thanks Art, I got it now. When they say NATO match, they mean for the Army and Marine teams in competition, which is in line with what Gus told me they did/do.

For everyone else, Hammonje is correct, just use the .308 gauges to check the chambers dimensions for NATO specs also. The bottleneck is 20 degrees on both chambers, so it is a simple matter of checking it's length from the bolt face to the bottleneck, it doesn't matter which gauge you use, see list above.

All of them have a 20 degree bottleneck, and measurements are taken at different datums or reference points on the bottleneck, for instance, .308 is taken at the .400 diameter of the bottleneck, NATO is taken at .013 further down the incline of the bottleneck "with the field gauge", hence the difference in the measurements and lengths of the SAAMI and NATO gauges, and the confusion. But it's actual headspace at the .400 datum, is the same as the .308. See in the drawing where it denotes the .400 diameter datum. It is the same measurements if you look at these drawings and the datums.

Only the military chambers are cut longer for debris in combat conditions. If you want your rifle ready for these type conditions, set it up between 1.6330-1.6355, if you want more of a match shooter only, set it up at 1.631-1.632 It doesn't matter which gauges you use to do it, as long as the length is right from the bolt face to the bottleneck at .400 datum. All headspace gauges, either NATO or commercial .308, are cut and made by referencing the datum at .400.

The measurements written on them, are from the rear to the datum at a diameter of .400 You can check this by taking a marks-a-lot and marking a line at the .400 width on the bottleneck using calipers, then measure with the calipers from the rear of the gauge, to the line, it should jive with the measurement written on the gauge.

Here's a goods article on it, it has a second page also if you click next at the bottom. Although he is a little more dramatic about it than is necessary.
http://how-i-did-it.org/762vs308/chamber.html
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  #37  
Old 11-20-2012, 11:31 AM
steelap steelap is offline
 
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Location: North AL
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Quote:
Originally Posted by hammonje View Post
Uh...why not just use 308 Win gauges like the rest of the world and MAKE LIFE EASY.

Unless you are trying to find out if a 7.62 NATO Navy B/R is in spec. I have been able to confirm headspace on every commercially built M14 I own with my Forster gauges so they must be OK. The armorers I know use 308 Win gauges, not 7.62 NATO.

Why do you guys want a 7.62 NATO chamber??????
Um, ... because I'm a tool-happy engineer?

My logic chain is like this, and I DON'T say it is correct, so feel free to pot-shoot it.

Looking at a Navy Mk2Mod1 BR:

1. I want to shoot .308 Win and suplus NATO 7.62x51 in it.

2. Requirements:

a. .308 Win - GO 1.630; NO GO 1.634; FIELD 1.638

b. 7.62x51 NATO - MIN 1.6355; MAX 1.6455

3. Logic - If I use a 7.62x51 MIN gauge (closes) and a .308 FIELD gauge (doesn't close), I should be good to go with both calibers.

Yes, No, Maybe?

"Life is Good!"
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  #38  
Old 11-20-2012, 11:34 AM
steelap steelap is offline
 
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Location: North AL
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Quote:
Originally Posted by nf1e View Post
When you get to estore click on .308 guages and you will see a photo. They are 7.62 Nato.
You are correct - they are marked for both (at least the NO GO gauge picture shows that).

"Life is Good!"
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  #39  
Old 11-20-2012, 11:38 AM
steelap steelap is offline
 
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Quote:
Originally Posted by M14 View Post
Your 1.6330 gauge is a perfect headspace by the way. I set all mine like Art at 1.6325, which is only one half thousandths less than your gauge. As I said before, it takes years of practice and many rifles checked, to learn the feel of one half a thousandths in your fingers.

For everyone else, Hammonje is correct, just use the .308 gauges to check the chambers dimensions for NATO specs also.

All of them have a 20 degree bottleneck, and measurements are taken at different datums or reference points on the bottleneck, for instance, .308 is taken at the .400 diameter of the bottleneck, NATO is taken at .013 further down the incline of the bottleneck "with the field gauge", hence the difference in the measurements and lengths of the SAAMI and NATO gauges, and the confusion. But it's actual headspace at the .400 datum, is the same as the .308. See in the drawing where it denotes the .400 diameter datum. It is the same measurements if you look at these drawings and the datums.

The measurements written on them, are from the rear to the datum at a diameter of .400 You can check this by taking a marks-a-lot and marking a line at the .400 width on the bottleneck using calipers, then measure with the calipers from the rear of the gauge, to the line, it should jive with the measurement written on the gauge.

Here's a goods article on it, it has a second page also if you click next at the bottom. Although he is a little more dramatic about it than is necessary.
http://how-i-did-it.org/762vs308/chamber.html
Sounds like I may have overbought. Oh, well, one of the hazards of being tool-happy (you should see my wood planes and wood chisel sets ).

I'll keep them, and put one set in my travel tools, and one set in the tool box.

"Life is Good!"
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  #40  
Old 11-20-2012, 11:43 AM
M14 M14 is offline
 
Join Date: Jul 2011
Location: south mississippi
Posts: 874
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Quote:
Originally Posted by steelap View Post
3. Logic - If I use a 7.62x51 MIN gauge (closes) and a .308 FIELD gauge (doesn't close), I should be good to go with both calibers.

Yes, No, Maybe?

"Life is Good!"
No. If you stay around 1.633, you can still use both calibers easily. Anything above 1.636 or so, will work your brass too hard if you reload. If you don't reload, don't worry about it, but still stay around 1.633-1.636

Here is why I say this:
I have checked thousands of cartridges that are new, of both calibers, 7.62 NATO and .308 commercial. They both average 1.627 for cartridge headspace. The recommended chamber headspace and area for expansion, is between .003 -.005, so at the max, that is 1.632, and min. is 1.630. So 1.633 should be perfect for any rifle to shoot both kinds of ammo. Just don't buy or use any foreign mil-surp, NATO or not. Unless, you check every cartridge for headspace first, and overall length. The length is the killer in foreign stuff. Like I always say, if you speak only English, and can't read what is written on the ammo case, don't buy it.
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