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i have a early fulton with a HR chrome lined barrel. now i know that there are differences (case vol/ pressure/ shoulder angle?) between 7.62nato and .308win.
so my question to the m14/ ma1 guru's... am i wrong in just using 7.62nato ammunition? or can i use .308win as well.
 

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A short explanation...

308 Winchester chambers have a slightly shorter headspace than true 7.62 NATO chambers.

Nearly all commercial M14's, even those with USGI barrels, will have the 308 Winchester headspace.

US military ammunition is manufactured to fit in either chamber. Some foreign military ammunition is too long for the shorter commercial chambers.

Commercial hunting ammunition will fit in your chamber, but may be too powerful for the operating system.
 

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What KurtC said is true, there is no difference between .308 Winchester and 7.62 NATO with regards to maximum chamber pressure. I have a Dept. of the Army manual dated April 1994 (TM43-0001-27) that states that the chamber pressure of 7.62 NATO ammo is 50,000 PSI, this is wrong, 7.62 NATO was originally measured using CUP (copper units pressure), a copper crusher system. It was wrongly transposed to PSI. If you google search SAAMI and look in the rifle cartridges section you will find that .308 Win and 7.62 NATO have the same pressure ratings. The issue with regards to M14 type rifles is that the gas system was designed to operate at, if I remember correctly, 12,500 +- 2,000 psi port pressure. This would mean that when handloading ammo you only have a certain area of applicable powders that will work and maintain that port pressure so as not to damage your gas system. And please, no offence to anyone but when will these myths finally die, it's almost as bad as the 5.56/.223 debate.

John
 

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What KurtC said is true, there is no difference between .308 Winchester and 7.62 NATO with regards to maximum chamber pressure. I have a Dept. of the Army manual dated April 1994 (TM43-0001-27) that states that the chamber pressure of 7.62 NATO ammo is 50,000 PSI, this is wrong, 7.62 NATO was originally measured using CUP (copper units pressure), a copper crusher system. It was wrongly transposed to PSI. If you google search SAAMI and look in the rifle cartridges section you will find that .308 Win and 7.62 NATO have the same pressure ratings. The issue with regards to M14 type rifles is that the gas system was designed to operate at, if I remember correctly, 12,500 +- 2,000 psi port pressure. This would mean that when handloading ammo you only have a certain area of applicable powders that will work and maintain that port pressure so as not to damage your gas system. And please, no offence to anyone but when will these myths finally die, it's almost as bad as the 5.56/.223 debate.

John
You'd think that if it really was an issue, Bill Wylde would have come up with a hybrid chamber type for the 7.62/.308 like he did for the 5.56/.223.
 

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Depends. The GI chamber is longer and some brass may not take the added stretch upon firing. UMC 308 Win did not work for me one time, several case head separations out of a box of 20.
 

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What KurtC said is true, there is no difference between .308 Winchester and 7.62 NATO with regards to maximum chamber pressure. I have a Dept. of the Army manual dated April 1994 (TM43-0001-27) that states that the chamber pressure of 7.62 NATO ammo is 50,000 PSI, this is wrong, 7.62 NATO was originally measured using CUP (copper units pressure), a copper crusher system. It was wrongly transposed to PSI. If you google search SAAMI and look in the rifle cartridges section you will find that .308 Win and 7.62 NATO have the same pressure ratings. The issue with regards to M14 type rifles is that the gas system was designed to operate at, if I remember correctly, 12,500 +- 2,000 psi port pressure. This would mean that when handloading ammo you only have a certain area of applicable powders that will work and maintain that port pressure so as not to damage your gas system. And please, no offence to anyone but when will these myths finally die, it's almost as bad as the 5.56/.223 debate.

John
I lament the re-classification of older versions of TM 43-0001-27 as Distribution A, and the book in general as a "technical manual". This is because as a technical manual, people erroneously use it as a source of technical information. It is intended as a source of logistical information, DoDACs and NSNs. It is NOT a good source of information regarding technical aspects of ammunition, pressures, velocities, sometimes even bullet weights, but especially charge weights.

To quote the stated purpose of the manual:

1-1. PURPOSE - This manual is a reference handbook published as an aid in planning, training, familiarization and identification of small arms ammunition, ranging from .22 Caliber to 30 millimeter and shotgun ammunition from .410 to 10 gage. This is the Federal Supply Class 1305. Operating instructions are are contained in the appropriate weapons manuals. (my emphasis)

The usefulness of TM 43-0001-27 in really limited to logistics planning.

If you want technical information of the characteristics of various ammunition, go to the actual military specifications, which unfortunately are not listed. (However, all but the latest are availble on line.)

SAAMI vs Military

Comparison between SAAMI and military pressure limits is near impossible due to the differences between methods used. For the longest time, the military has measured chamber pressure at case mouth, whereas SAAMI listed the limits at mid-case, there is no fixed correlation between these two. However, the military does use mid-case pressure values on occasion for research and development testing, so we do have historical samples of mid-case pressures for various lots of ammunition. None of these have ever exceeded SAAMI limits, so it is a safe assumption that military is "safe" in all firearms that will actually chamber it.

There are other differences between the the two requirement standards, the military listing the average chamber pressure and limiting the extreme ends of the distribution curve by limits on the standard deviation, SAAMI limits the maximum average chamber pressure and limit the distribution by the Maximum Probable Lot Mean (MPLM) and Maximum Probable Sample Mean (MPSM) which are defined in SAAMI Z299.4.

And last, there is the actual chamber of the pressure test barrel. The SAAMI requirement for the pressure test barrel chamber is the standard chamber for .308 Winchester made to the minimum size. The military pressure test barrel chamber is unique to the velocity and pressure test barrel. (And BTW, that chamber has no leade or freebore, the forcing cone starts at the termination of the case neck.)

Port Pressure

The specified port pressure for 7.62mm ammunition is taken at 15 inches from the breech face. This is not the location of the port in the M14, M60, or M240. So please do not make the error of thinking that a port pressure in excess of 14,500 psi* is damaging to your M1A/M14.

_ _ _ _ _ _ _
* This was the highest listed port pressure limit, and should be noted is a C.U.P. measurement. The current specified port pressure limit for M80 Ball ammunition is 9,150 to 12,650 psi.
 

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Lysander , you are a wealth of info ,I hope you don't mind ,I copied your response & filed it . For future reference of course . This subject comes up from time to time with people I work with , as does the .223/5.56 debate . I have always told them , they don't make 7.62x51 Die sets , not commercially that is , none I have seen in all my years of reloading .

Thanks
 

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With regards to the .223/5.56 issue, I spoke with a gentlemen yesterday, by his hat he was a Vietnam vet, that said "you shouldn't shoot 5.56 ammo in a rifle chambered for .223" that the gun would blow up. I told him to my knowledge the only difference between the two was a little more generous throat area, headspace was the same. He stated that 5.56 was higher pressure, I just checked with SAAMI and they don't list the 5.56 cartridge, they list the .223 Remington at 52K CUP and 55K PSI. The following article explains the different methods used to obtain pressure readings and why people think the 5.56 round operates at higher pressures.

223 REMINGTON AND THE 5.56X45mm MILITARY/NATO CARTRIDGE AND CHAMBERS « Western Powders

John
 

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With regards to the .223/5.56 issue, I spoke with a gentlemen yesterday, by his hat he was a Vietnam vet, that said "you shouldn't shoot 5.56 ammo in a rifle chambered for .223" that the gun would blow up. I told him to my knowledge the only difference between the two was a little more generous throat area, headspace was the same. He stated that 5.56 was higher pressure, I just checked with SAAMI and they don't list the 5.56 cartridge, they list the .223 Remington at 52K CUP and 55K PSI. The following article explains the different methods used to obtain pressure readings and why people think the 5.56 round operates at higher pressures.

223 REMINGTON AND THE 5.56X45mm MILITARY/NATO CARTRIDGE AND CHAMBERS « Western Powders

John
Everything noted about the 7.62mm/.308 Winchester also applies to the 5.56mm/.223 Remington regarding specified pressure limits, test procedures and test barrel chambers. . .

-HOWEVER-

The difference in throat dimension of the M14 chamber and the SAAMI .308 Win chamber is not as severe as that of the M16 chamber and the SAAMI .223 chamber. The leade length for the various chambers:

M14 = 0.174"
.308 = 0.090"
M16 = 0.085"
.223 = 0.025"

While the difference in leade length is greater for the M14-.308 (0.084" vs 0.060") it is important to note the SAAMI leade is quite generous for .308 Winchester, whereas the SAMMI .223 Remington chamber has a very short lead of 0.025", so the addition of 0.06" will reduce the peak pressure quite a bit. Some tests have shown that there is a 5,000 to 7,500 psi peak pressure increase shooting military M855 in a SAAMI cut chamber. An extra 7,500 psi will not likely blow up your gun, but it is certainly not a recommended thing to do on a regular basis.


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"Just because two things look similar on the surface, does not mean that assumptions safe for one, apply to the other. It is essential that all factors be considered."
-Anymouse-
 

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I have always told them , they don't make 7.62x51 Die sets , not commercially that is , none I have seen in all my years of reloading .
The nominal dimensions for the 7.62mm NATO case and .308 Winchester case are identical, there are a few tolerance differences, but none that would prevent a chamber that accepts one from accepting the other. This is also true between the 5.56mm NATO case and .223 Remington case.
 
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