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Thread: .308 Winchester vs. 7.62x51 mm pressure

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    .308 Winchester vs. 7.62x51 mm pressure

    I was talking to a friend today and he found some information on the errornet that stated that the commercial .308 Win ammo is loaded to higher pressures than military 7.62 x 51 mm (NATO) ammo.

    I was always under the impression that this was the reverse as proven by the generally thicker base of the military cases. Can anyone point me to a difinitive reference on this (one way or another)? TIA.
    Last edited by CarlosDJackal; 01-01-11 at 20:30.
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    I had heard this too before, but I can't remember where. With a quick search, I found the following website. I don't know that it could be termed 'definitive' or not, but until someone tells me this site is often erroneous I will continue to find it useful.

    http://www.6mmbr.com/308win.html

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    7.62 NATO is lower pressure than .308 Winchester.
    I'm an FFL/gunsmith, not the holster company.

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    The SAMMI/CIP maximum pressure for the .308 Win cartridge is 62,000 psi, while the 7.62x51 max is 50,000 psi

    http://www.6mmbr.com/308win.html

    See it has already been posted by PlatoCATM
    Last edited by Thomas M-4; 01-01-11 at 23:31.

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    That's interesting because I remember another website that states the opposite max pressure. I'll have to keep digging.
    We must not believe the Evil One when he tells us that there is nothing we can do in the face of violence, injustice and sin. - Pope Francis I

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    .308 is higher pressure than 7.62N. I dont have the link to back it up but ive looked it up before.

    SAAMI and MIL pressures are measured in different places IIRC so thats why you may see some literature list 7.62N as higher pressure.
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    7.62 NATO and 308 Win have about the same maximun chamber pressure. You cannot directly compare the way CIP measures pressure to SAAMI to NATO, so the often cited differences are apples to oranges. I have written to many ammunition companies and even makers of pressure testing equipment to confirm this.

    You do have to be careful about the pressure curve, the 7.62 N normally uses relatively fast powders and the gas port pressure so the gas port pressure is kept at bay. Some 308 can be loaded with slow powders (specially the "light magnum" kind of loads), and thus the port pressure can be vastly different with functional/durability problems in some guns.

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    They could be confusing the 308/7.62 with 5.56 and 223. 308 is higher than 7.62 and 5.56 is higher than 223.

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    My understanding has always been that 7.62 was lower pressure than .308. Generally speaking, he thicker case on 7.62 means less powder.

    This is somewhat counterintuitive since 5.56 is generally a higher pressure than .223.

    This should not be construed as saying that .308 is "better" than 7.62. Especially if you reload the .308 brass might be considered to be more likely to rupture or do other bad things.

    I think TiroFijo is pretty spot on.
    Last edited by Gutshot John; 01-02-11 at 19:43.
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    Quote Originally Posted by CarlosDJackal View Post
    I was talking to a friend today and he found some information on the errornet ...
    Should have stopped him right there. It's an Internet Rumor that just won't die.

    You cannot compare the military measurement, which is 52,000 PSI with the copper crusher gauge to the SAAMI 62,000 PSI which is a piezoelectric transducer gauge measurement.

    Military measurements in CUPs VS SAAMI in (piezo) using other calibers such as the 30-06 show about the same spread.

    In reality, Max pressure for .308 and 7.62x51 are about the same.

    DIE RUMOR DIE!

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    So does this mean that .223 and 5.56 are also about the same?
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    Quote Originally Posted by Gutshot John View Post
    So does this mean that .223 and 5.56 are also about the same?
    Nothing to do with .223 VS 5.56. The freebore is considerably longer in 5.56 NATO which is the major issue between the two.

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    Here's an article that goes into pretty good detail about the differences between the two. http://how-i-did-it.org/762vs308/

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    Quote Originally Posted by shootist~ View Post
    Should have stopped him right there. It's an Internet Rumor that just won't die.

    You cannot compare the military measurement, which is 52,000 PSI with the copper crusher gauge to the SAAMI 62,000 PSI which is a piezoelectric transducer gauge measurement.

    Military measurements in CUPs VS SAAMI in (piezo) using other calibers such as the 30-06 show about the same spread.

    In reality, Max pressure for .308 and 7.62x51 are about the same.

    DIE RUMOR DIE!
    Now this makes sense and basically goes with what I had always been told. The difference is that a lot of commercially available .308 ammo are loaded towards the low-end of the pressure spectrum to mitigate the big "L". This practicereduces the possibility of causing some cheaply made commercial gun to go "boom". Not much of an issue for the military.
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    Quote Originally Posted by CarlosDJackal View Post
    Now this makes sense and basically goes with what I had always been told. The difference is that a lot of commercially available .308 ammo are loaded towards the low-end of the pressure spectrum to mitigate the big "L". This practicereduces the possibility of causing some cheaply made commercial gun to go "boom". Not much of an issue for the military.
    Speer reloading manual that I have states that .308 is rated to higher pressure [does this make it true no but I would not totally discount it neither].
    http://www.thegunzone.com/30cal.html
    I cant vouch for the accuracy but they state that both have been measured by transducer .308 and 7.62 and the .308 is rated to higher pressure.
    My personal thought is that light magnum loads that are loaded with slower burning powder run at max press but these loads are not recommended for autoloading rifles.

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    The thing that makes the most sense of all is to check the headspace of any surplus rifle to make sure its not on the loose side. (And don't just use a military "field" gauge to do it.)

    Even so, I've always considered the thicker Mil brass to be safer in my FALs even though I've personally set the headspace to fall between SAAMI/.308 and FN/7.62x51 minimums (or at least below a US NOGO gauge.

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