Cartridge & Headspace Specifications: .308 Win / 7.62 NATO

[normannewguy]

Ok, here are the specs again...

SAAMI .308 Winchester:
GO: 1.630 in.
NO-GO: 1.634 in.
FIELD: 1.638 in.

FN FAL:
GO: 1.6325 in. (FN & Brit/commonwealth. Canadian is 1.6315 in.)
NO-GO: 1.638 in.
FIELD: 1.640 in.

7.62 NATO (M14 US MILSPEC):
GO: 1.6355 in.
NO-GO: 1.638 in.
FIELD: 1.6445 in.

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Chamber and cartridge drawings...

1. .308 Winchester:
Direct link: http://s1052.photobucket.com/user/f6...tml?sort=3&o=2





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2. 7.62 NATO:
Direct link: http://s1052.photobucket.com/user/f6...tml?sort=3&o=3




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Both cartridges have the exact same external dimensions! The only difference between the two is usually the weight of the brass (generally due to thicker brass near base on NATO cartridge)...
- .308 Win SAAMI brass weighs in average between 155 - 165 grains.
- 7.62 NATO brass weighs in average between 175 - 188 grains.

Looking at the GO for SAAMI and NATO there is a .005 difference, which means there will not be a problem in using 7.62 NATO ammo in a .308 chamber.
Most US ammo companies who make NATO ammo (Winchester being one) produce to the minimum spec of 1.628 and hold it there, which allows it to be chambered in both.

The only time you run into a problem is overseas ammo companies who make ammo to NATO standards. They will let stuff go that headspaces at 1.633 to 1.635 which in a 7.62 NATO chamber is fine, but is .003 to .005 too large for a .308 Win chamber.

If you have a minimum chamber of 1.630, you can run into feeding problems with some NATO spec ammo but normally only overseas stuff, like PPU.

[Big_Red]

All,
Worked with normannewguy to make his post a sticky...many thanks to him for providing this data!

Regards,
Rob

[sapishka]

the NATO case is thicker and much more so near the base ,so if you cut the 2 open down the middle the difference between the 2 is readily apparent .something that is rarely ever discussed about these two cartridges ,NATO brass is thicker brass .AND so .. the sentence posted IS the issue ..the stuff that headspaces at 1.635 and is too large for a 308 win chamber . lots of NATO ammo still available and still being used so best to use the correct ammunition in your rifle .


sapishka

[normannewguy]

Originally Posted by sapishka

the NATO case is thicker and much more so near the base ,so if you cut the 2 open down the middle the difference between the 2 is readily apparent .something that is rarely ever discussed about these two cartridges ,NATO brass is thicker brass .AND so .. the sentence posted IS the issue ..the stuff that headspaces at 1.635 and is too large for a 308 win chamber . lots of NATO ammo still available and still being used so best to use the correct ammunition in your rifle .


sapishka

Ok I guess you missed the part where I said NATO brass is heavier than 308 WIN commercial.
Also I think you missed the part where I said most US manufacturers hold NATO brass to min specs 1.628 and some overseas companies who make to NATO standards slighty larger 1.633 or so can have problems in 308 WIN chambers.
So I am not sure if you read the machinist drawings that were provided. Dimensionally they are the same, except like I said some overseas PPU being one making ammo that headspaces at 1.633.

[sapishka]

you said heavier ,I said thicker and internally dimensionally different ,I agree with your other statements ,no argument ,they actually make the point quite clearly ,NATO 7.62x51 abounds and is available from many countries as surplus ,not for 308 chambers due to headspace as you have pointed out .Again ,no argument ,I did not miss anything you had said ,however ,I do have my own information and thoughts to add to this ,which are correct .

sapishka

[normannewguy]

Originally Posted by sapishka

you said heavier ,I said thicker and internally dimensionally different ,I agree with your other statements ,no argument ,they actually make the point quite clearly ,NATO 7.62x51 abounds and is available from many countries as surplus ,not for 308 chambers due to headspace as you have pointed out .Again ,no argument ,I did not miss anything you had said ,however ,I do have my own information and thoughts to add to this ,which are correct .

sapishka

Ok the specification for NATO on headspace is 1.634 -.006. Which means that anything from 1.628 to 1.634 is acceptable. So like I said Winchester, Federal, Lake City and the like normally headspace at 1.628. So does Radway, German and the like. They will work in 308 WIN chambers no problem whatsoever. Now occasionally you will get stuff like PPU or Indian ammo that headspaces at 1.633. In a tight 308 WIN chamber yes you will have issues.
On NATO brass the webbing is thicker due to intended use in full auto weapons. Hence they are heavier. Does that make a difference in semi auto or bolt guns, no. Its heavier due to intended use in weapons that headspace all the way up to 1.6445. It has to work once and that's all the military asks of it and go bang and be extracted. Can you use 308 WIN in NATO chamber? Yes of course, but brass life is very short.
Please add your info would love to see it if there is any difference to what I have posted.

[sapishka]

Well its like those of us with the NATO chambered Garands, we have to measure the headspace right off upon receiving one of these fine Garands and mine spec'd out as new. However a lot of guys have had to find bolts that brought the headspace to the GO spec to 1.635 which is the as-new manufactured NATO SPEC chambering of these rifles. Match grade type A and B rifles are excluded as those readily spec out tighter chambers and can use 308 win cartridges with no headspace issues. Your findings are correct as I see them on specs and what works and where, so the differences are the headspacing you've covered. The shooter just needs to be aware "if possible" of which ammunition he or she is shooting in the rifle they are using. There is the whole talk about pressures to speak of which has been covered many times over and the cause of too many consternating arguments, so not going there, but looks solid here on the information provided .


sapishka

[normannewguy]

Originally Posted by sapishka

well its like us guys with the NATO chambered Garands ,we have to measure the headspace right off upon receiving one of these fine Garands ,mine speced out as new. however a lot of guys have had to find bolts that brought the headspace to the GO spec to 1.635 which is the as new manufactured NATO SPEC chambering of these rifles ,Match grade type A and B rifles excluded as those readily spec out tighter chambers and can use 308 win cartridges with no headspace issues .your findings are correct as I see them on specs and what works and where ,so the differences are the headspacing you've covered ,the shooter just needs to be aware "if possible" which ammunition he or she is shooting in the rifle they are using is correct for it .theres the whole talk about the pressures to speak of which has been covered many times over ,and the cause of too many consternating arguments ,so not going there ,but looks solid here on the information provided .


sapishka

Ok you missed it again, both 308 WIN and 7.62 NATO are the same period. The headspace specifications for the cartridges are SAMMI 1.627- 1.634, NATO 1.628-1.634. The only reason NATO went to the larger chamber was for battlefield reliability, (full auto weapons ,M14 M60, headspace does decrese under full auto fire) and the chambering issues with dirty weapons and ammunition. You can shoot 308 WIN in a NATO chamber no problem at all. If you reload tho only expect maybe 2 reloads out of it before it rips in half because of the lighter webbing, remember weight of brass or did we miss that also?
The US military spec for 7.62 NATO is 50,000 PSI, now SAMMI max for 308 WIN is 62,000 PSI. Now is any 308 WIN FMJ or Match ammo loaded to this spec, no. Oh and there is no machine gun ammo that has higher pressures, sorry its all M80 or M59 ball.
The only NATO round you might have to worry about for pressure is M118LR made prior to 2005 in air temps above 120 F as due to the powder and temps these became very powerful and damaged M14 in IRAQ.
So to all those people who thought they had to bring it out to headspace of 1.635, they were wrong. They didn't have to at all. If it headspaced at 1.633 they were fine for both 308 WIN and 7.62 NATO
BECAUSE THEY ARE THE SAME SIZE

[raymeketa]

Originally Posted by normannewguy

. . .The only NATO round you might have to worry about for pressure is M118LR made prior to 2005 in air temps above 120 F as due to the powder and temps these became very powerful and damaged M14 in IRAQ. . . .

I've heard that same thing more than once but cannot come up with any hard evidence to support it. The first Gulf War took place in 90/91 and the Iraq War in early 2003.The hot M118LR was only loaded from 1995 to 1999. It was intended only for bolt guns, particularly the M24 and M40 snipers. I doubt if the average GI with an M14 would have had access to it. By the time ATK took over operation of the LCAAP in 2001, the load had been reduced to what we have today.

One of the major reasons for reducing the load was, I believe, the considerable investment in sights, especially the USMC Unertls. They were developed based on the trajectory of the old M118 Match and the hot M118LR was an unacceptable mis-match.

But, I'm always willing to learn. And I've changed my opinion on a lot of things.

JMHO

Ray

[Big_Red]

Alright, cleaned up as best I could without losing the gist of the point/counter-point, which ironically are the same and support each other, i.e.--the NATO brass is heavier because it is often thicker (NOT wider), particularly near the base. Also confirms the exterior dimensions of each cartridge are the same. As clearly noted, it is the length of the chambers that can differ.
Words were getting in the way of the message.

I've modified the OP to clarify the exterior dimension point, and worked with Norman to actually post the dimensions themselves so they are right there for everyone to see/reference.

For supplementary info, when I get a chance, I will pull down a NATO cartridge and a SAAMI cartridge (each from the same respective lot), then fire another one of each from the same rifle, then cut the brass in half of all 4to compare and demonstrate graphically the similarities as well as the difference in thickness.
If someone already has that, please...post away.

And please note that any further posts that are purely subjective speculation and/or derailing the thread will be deleted.

Thanks for your support.