7.62x51mm NATO vs .308 Win.

This is a discussion on 7.62x51mm NATO vs .308 Win. within the Defensive Rifles & Shotgun Discussion forums, part of the Related Topics category; Originally Posted by Thanis Can anyone clarify this for me: 7.62x51mm NATO or 308 Winchester? What's the Difference? "The worst case scenario for shooters of ...

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Thread: 7.62x51mm NATO vs .308 Win.

  1. #16
    VIP Member Array Rob72's Avatar
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    Quote Originally Posted by Thanis View Post
    Can anyone clarify this for me:

    7.62x51mm NATO or 308 Winchester? What's the Difference?

    "The worst case scenario for shooters of 7.62 NATO rifles is as follows: Using a commercially made, maximum pressure cartridge with long headspace, fired from a weak action (ex. converted 93/95 Mausers)."

    What?

    "The weaker action is a possible final piece of the 308 vs 7.62 NATO puzzle."

    What?
    First, know your source- in this case a surplus (specifically bolt action) rifles forum. IOW, they are talking about using modern .308 Win (high pressure) in an 1890's receiver that is only surface hardened. It has nothing to do with semi-autos made in the last 40 years (aside from possibly some surplus M1A kit guns).

    In practical terms, the difference is more in which chamber will allow which round(s) to chamber fully. In a US-made weapon, if you intend to strictly shoot US made factory ammo(shooting for accuracy), look for "Match chambered"; if you want to shoot surplus/whatever you have(accuracy is necessary, but less critical than being able to shoot something), get "mil-spec" or 7.62x51 N.

    This is really the key point from RR's link:
    1. Winchester 308 For modern sporting rifle post 1952
    2. NATO For Military rifle post 1952
    3. CETME Spanish Mauser

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  3. #17
    Member Array Darth AkSarBen's Avatar
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    On my Saiga .308 it has both .308 Win and 7.62 x 51 stamped on the right side. Even though it is primarily a .308 Winchester chamber, it should also feed and fire safely the lower pressure 7.62 x 51.
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  4. #18
    Senior Member Array tankdriver's Avatar
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    Read a reloading manual. Same powder same load. Same thing.......

    From DSA who makes the FN FAL's in the US

    8- Should I use .308 win ammo or 7.62 nato in my FAL?
    It is ok to use either type as the difference is only approximately .003" chamber dimension.
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  5. #19
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    For years I have heard it both ways.

    I been using both, interchangeably for about 40 years with no issues.

    Most chambers aren't even chambered close enough to matter. Take two identical rifles and you'll get several thousandths of difference on both head space and even diameter due to different reamers being used.

    Does it matter in print? Many would say so.
    Does it matter in real life? Many that have used them both would say no.
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  6. #20
    Member Array Mr. Habib's Avatar
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    There is a lot confusion about chamber pressures when comparing .223 vs 5.56 x45 and .308 Win and 7.62 x 51. SAAMI measures chamber pressure at the midpoint of the case, the military measures at the case mouth. The readings are NOT directly correlated or interchangeable. Just because the SAAMI max pressure is higher or lower than the military pressure doesn't make one combination safe or unsafe. Other factors like freebore length have to accounted for.

  7. #21
    Distinguished Member Array jumpwing's Avatar
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    The next rifle I get will most likely be in the .30-range; this is good info but I don't see a conclusion (unless I missed it).
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  8. #22
    Senior Member Array tankdriver's Avatar
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    Quote Originally Posted by Mr. Habib View Post
    There is a lot confusion about chamber pressures when comparing .223 vs 5.56 x45 and .308 Win and 7.62 x 51. SAAMI measures chamber pressure at the midpoint of the case, the military measures at the case mouth. The readings are NOT directly correlated or interchangeable. Just because the SAAMI max pressure is higher or lower than the military pressure doesn't make one combination safe or unsafe. Other factors like freebore length have to accounted for.
    Also one is pizzo PSI the other is CUP PSI. They will never read the same.

    http://www.thegunzone.com/30cal.html

    The .308 Winchester and the 7.62mm NATO (nee T-65) cartridges are not the same, nor should they be considered interchangeable despite apparently identical external dimensions… the chamber drawings are in fact different.

    But as Clint McKee and Walter Kuleck of Fulton Armory note on their "award-winning" website:
    They are the same, 'cause nobody makes 7.62mm (NATO) ammo that isn't to the .308 "headspace" dimension spec. So 7.62mm ammo fits nicely into .308 chambers, as a rule.
    While the 7.62mm NATO cartridge has a maximum chamber pressure of approximately 50,000 pounds per square inch (psi), in the SAAMI book the .308 Winchester has a MAP (maximum average product) pressure of approximately 62,000 psi* (each by conformal transducer measurements, and therefore comparable). This is not to say that all .308 Winchester loads will develop such pressures, merely that they would be within manufacturing tolerances if they did so. Firing .308 Winchester ammunition in a firearm specifically chambered for the 7.62mm NATO risks damage to the firearm and injury to the shooter.

    A 7.62 NATO Go gauge is .003-inch longer than a .308 Winchester Go gauge. The 7.62 NATO NoGo is also longer, to the tune of .004-inch. It's entirely possible to chamber and have an accident with a .308 Winchester round in a rifle that would be safe for 7.62 X 51mm. A chamber in 7.62 that could barely close on a 7.62 NoGo could swallow a .308 Field gauge. Add to this the fact that .308 Winchester brass, being of commercial manufacture, is much thinner than that of the 7.62 NATO, and expands alot more, could possibly lead to casehead separation.

    And just when we thought that we had this 7.62mm NATO stuff down pretty pat, along comes Adam Firestone at Cruffler.com with his taste for the arcane, who makes a compelling brief that much of what many thought they "knew," was all wrong! An excerpt:

    Many shooters are aware of the differences between the dimensionally similar 7.62mm NATO cartridge and the .308 Winchester. What most are not aware of is that all cartridges called "7.62mm NATO" are not created equal, and that there is significant variation, both dimensionally and ballistically, between 7.62mm NATO cartridges as manufactured by different countries, and even between such cartridges as manufactured by different arsenals within the same country. As a result, the terms "NATO spec" or "NATO standard," which imply that all "NATO" cartridges are the same or to indicate the fitness of given 7.62x51mm ammunition for a specific use, are misleading.


    * - This translates to approximately 52,000 cup (Copper Units of Pressure).
    Chamber Headspace Gauges
    .308 Winchester
    GO: 1.630"
    NOGO: 1.634"
    FIELD REJECT: 1.638" 7.62 x 51mm NATO
    GO: 1.635"

    FIELD REJECT: 1.6455"
    Chamber Pressures
    .308 Winchester
    MAP: 62,000 psi
    MPSM: 66,000 psi
    Minimum Proof Pressure: 83,000 psi
    Maximum Proof Pressure: 89,000 psi 7.62 x 51mm NATO
    Maximum: 50,000 psi

    Proof pressure: 67,500 psi
    Sources: .308 Winchester data from ANSI/SAAMI document Z299.4-1992, Pressure and Velocity, Centerfire Rifle Sporting Ammunition

    7.62 x 51mm NATO headspace data from Jerry Kuhnhausen's M1/M1A shop manual.

    Pressure data from TM 43-001-27: Army Ammunition Data Sheets Small Caliber Ammunition
    According to Ken at Clymer Tools, noted maker of headspace gauges, the problem isn't the round itself, it's the headspacing.
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