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Discussion Starter · #1 ·
Is there a difference between the chamber on a USGI chrome-lined barrel and the chamber on a Commercial barrel if they are both headspaced to the same dimension usch as 1.6315?

I don't quite understand the relationship between chamber and headspace, especially in regards to the difference between a USGI chamber and a commercial one. If the GI is for 7.62 NATO and the commercial was for .308 does it make any difference if they are both headspaced to 1.6315?

What's the relationship here?
 

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:D Yes there is, go to Fulton Armory and look in their FAQ, there is an Article on it. :)
 

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Discussion Starter · #3 ·
I read the article and I understand the difference between .308 and 7.62 fundamentally. I understand that there are different GO, NO GO, and FIELD specs for 7.62 and .308 but that they are essentially the same except that NATO is longer and it is unsafe to fire .308 in a 7.62 NATO chamber.

1) I am talking specifically about the physical characteristics of a USGI chrome lined barrel chamber compared to a commercial barrel that are both headspaced to the same exact dimenstion of 1.6315. In other words, if they have the same headspace what difference does it make whether the barrel was constructed by the US gov't or a commercial maker, aren't they the same thing?

2) Furthermore, if the minimum headspace for USGI is 1.64 and the maximum for .308 is 1.64 how is it safe to make a rifle that fires both.

How do you get around the fact that 1.6315 is way under spec (1.64) for USGI ammo, yet it is safe to use surplus ammo? Doesn't that defy what the NATO specs say? Why doesn't the NATO spec start at 1.630 if that was safe for surplus ammo?
 

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:? That is something for Warbird or Ted Brown to answer, all I can tell you is that I have shot .308 in 7.62X51 and visa versa for 35+ years and my Rifles and I have not suffered! ;)
 

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M1A Owner,

While I'm not an expert on headspace, the answer to your last question is the way I see it is that the Nato spec headspace is longer because of battlefield conditions and dirty chambers. The increased headspace increases reliability which is important on the battlefield. To help prevent case head separations due to increase strecthing of the case, the Nato case walls are thicker. That reduces the internal dimensions of the case and is the reason why the reloading manuals reccomends that you reduce the powder charge when using military cases.

Since my rifle uses are civilian in nature, I prefer the commerical spec. There is less chance of case head separations and the cases lasts more reloadings.

One draw back I see to the shorter commerical specs would be a possibility of a out of battery firing. With clean chambers, I believe that would be very remote.

Hopefully Warbird and some of the others can chime in and help us all to better understand headspace and the differences between the commerical and Nato spec.

Joe A.
 

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I think you pretty much nailed it Joe A. . The difference in outside dimensions are very close on NATO and 308 Win. . Battle rifles need to go bang every time, commercial chambers will go bang every time with standard cleaning habits and not trying to see how many twenty round mags you can dump in a half hour :arm15: . Your chamber is cut fine unless you plan on abusing your rifle for no apparent reason or decide you want to do some belly crawling through the mud before your range session.
 

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Discussion Starter · #7 ·
So, if I just bought 2 brand new completely unused barrels, one that is a chrome lined USGI and the other a commercial non-chrome lined. If I put these side by side and measured them, never having been used before, the chambers would be identical?
 

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M1A_Owner said:
So, if I just bought 2 brand new completely unused barrels, one that is a chrome lined USGI and the other a commercial non-chrome lined. If I put these side by side and measured them, never having been used before, the chambers would be identical?
My guess would be no. Some (or most, or all?) non-chrome Commercial M14 barrels come with short chambers that need to be finished reamed after its installed on a receiver.
 

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Maybe this will help.

For the .308 Winchester: GO gage (or minimum headspace) is 1.630"

NO GO gage (maximum for initial barreling/cutting of headspace) is 1.634"

Field Reject gage (or the maximum headspace) is 1.638"


For the 7.62mm: GO gage is 1.634" (the same as NO GO for the .308 Win.)

NO GO is 1.638" (the same as the Field Reject for the .308 Win.)

The Field Reject is 1.6445"

Headspace on a commercial barrel from the manufacturer is usually cut short, and the final cut is done after the barrel has been installed.

Headspace on a GI barrel cannot be cut after it has been chrome lined and is adjusted by changing to a longer or shorter bolt. Installing a new GI barrel will usually be in spec using the existing bolt, but should always be checked with headspace gauges just to make sure before firing.
 

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Joe A. said:
M1A Owner,

While I'm not an expert on headspace, the answer to your last question is the way I see it is that the Nato spec headspace is longer because of battlefield conditions and dirty chambers. The increased headspace increases reliability which is important on the battlefield. To help prevent case head separations due to increase strecthing of the case, the Nato case walls are thicker. That reduces the internal dimensions of the case and is the reason why the reloading manuals reccomends that you reduce the powder charge when using military cases.

Joe A.
That's about right and not much I could add at the moment.
This could apply to chromed and non chromed barrels.

Non chromed barrels can be headspaced either way but, usuallly their done on the tight side to get better accuracy like match rifles.
Match or sniper rifles are usually better maintained due to their purpose.

Even though reloading manuals have gotten very conservative on powder charges in recent years, the individual companies suggest starting at a 10% reduction when using military brass as compared to commercial brass.


 
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