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Difference between 7.62 and .308?

Discussion in 'Rifle Country' started by jtheise4, Sep 16, 2009.

  1. jtheise4

    jtheise4 New Member

    Mar 20, 2009
    Can someone please explain the difference between a 7.62 and a .308? Are they interchangable? Can a .308 be shot in a rifle chambered for 7.62, in the same fashion a .223 can be shot in a 5.56 rifle? Thanks for the input.
  2. NCsmitty

    NCsmitty Mentor

    Jun 29, 2008
    North Carolina
  3. Mr_Pale_Horse

    Mr_Pale_Horse Active Member

    Nov 27, 2007
    Ball versus Commercial:

    Ball, or a military designation, is loaded to a specific Overall Length, Bullet Weight and Ogive (shape) and powder burn rate that allows it to work in self loaders (gas operated, long and short recoil, etc). Ball often is made with thicker cases that hold less powder, but stand up better to the mechanical stresses that self loaders dish out.

    When Ball crosses over to a commericial cartridge, you end up with issues that are unforeseen. A commercial cartridge may be overlength or use too slow a powder to work in a self loading military design. A Ball cartridge may generate higher pressures in a tight commercial target rifle or a short throated target bore.

    In general, they will work, but as a general rule:

    1. I will use Ball and Commercial interchangeably in sturdy bolt action or other strong, manually cycled actions, which tend to be overbuilt and rather loose in dimensions, AND are labeled for interchangeability.

    2. I will only use the specified Ball in military (style) or other self loaders.

    3. I will only use the Ball or Commercial round specifically called out on Target rifles.
    Last edited: Sep 16, 2009
  4. cuervo

    cuervo Active Member

    Jan 12, 2005
  5. 9mm+

    9mm+ Active Member

    Aug 12, 2009
    Cary, NC
    Pale Horse's explanation of .308 vs 7.62 is excellent (as well as the links the others provided). With the ammo shortage still dragging on, it's tempting to shoot military rounds in commercial rifles, but I wouldn't advise it.
  6. USSR

    USSR Mentor

    Jul 7, 2005
    The primary difference is the slightly different allowances for chamber dimensions (7.62x51 chamber dimensions can be more generous). The external dimensions for the cases are identical (Note: there are no 7.62x51 dies sold). There is also a slight difference in maximum pressure allowances between the two cartridges (.308 allows for slightly more pressure), but you cannot directly compare the two, since one (7.62x51) was measured by the gov't using the copper crusher method, and the other (.308) was measured by SAAMI using the piezoelectric method. Interchangeability is a function of the platform in which they are to be used. If the firearm was developed to operate within certain pressure spec's, such as the M1 Garand with it's port pressure limitation, then .308 should not be used unless the ammo conforms to the Garand's ammo rules (no powder faster than IMR3031 or slower than IMR4320, and no bullet heavier than 180 grains). In modern bolt action rifles, the ammo is essentially interchangeable.

  7. Norinco982lover

    Norinco982lover Active Member

    Mar 14, 2008
    South Central Kansas
    What about say....a Saiga .308? Could you use both?
  8. malix

    malix New Member

    Aug 27, 2006
    Cleveland Ohio
  9. longdayjake

    longdayjake Senior Member

    Apr 10, 2008
    Genesee, ID
    yes you can use both. There are no issues with interchanging .308 and 7.62. The only difference is case thickness.
  10. jonnyc

    jonnyc Senior Member

    Dec 5, 2004
    SE Pennsylvania
    The only difference is INTERNAL case thickness. Factory ammo, called either 7.62 or .308, is completely interchangeable. Reloaders need to watch hot .308 loads in military cases. Any info to the contrary is nothing but internet drivel.
    Last edited: Sep 16, 2009
  11. TheResearcher

    TheResearcher New Member

    Sep 13, 2009
    Belvidere NJ
    Will the Kel Tec Su16 fire .223 and 5.56? Sorry I was this close to under standing the fulton-armory and I lost it.
  12. Bart B.

    Bart B. Participating Member

    May 20, 2008
    Military rifle teams have put thousands (millions?) of rounds of ammo through theie M14's and 7.62 NATO converted M1 Garands. Both commercial factory match loads and military arsenal match loads. And they've shot both types in Winchester and Remington bolt action match rifles. No incidents whatsoever.

    Stiffest load used in any was 44 grains of IMR4320 in a primed LC match case under a Sierra 190. Best long range load for Garands used by USN and USAF teams in the world. USMC and Army teams liked pulling the 172-gr. bullet from M118 match ammo then seating a Sierra 180 HPMK in it for their long range load in M14's. All the services pulled the 147 bullet from M80 ball ammo loaded with extruded powder (IMR4475) then seated a Sierra 168 in them; a load that equalled blue pill pressure test loads. But it was also extremely accurate through 600 yards.
  13. mongo4567

    mongo4567 Active Member

    Oct 3, 2008
    My only concern with the interchangibility is with what I consider to be rifles that are marginal for the caliber. The Spanish Mausers converted to 7.62 with questionable heat treating and a weaker small ring mauser action with one less locking lug for example. The little extra pressure that a commercial .308 round generates isn't something that I want to put next to my face....but I wouldn't be shooting that particular rifle with 7.62 NATO either.
  14. Candiru

    Candiru Member

    Feb 1, 2005
    The biggest issue with 7.62x51mm vs. .308 isn't so much the pressure as the chamber dimensions. 7.62x51mm chamber spec for NO-GO is still larger than .308 GO. That's why military rounds have thicker brass: so that there's more material around the web of the case to prevent head separation in such a loose chamber. (The thicker case brass is probably part of what contributes to the myth that the two round have vastly different pressures, as reloading manuals will caution the user to reduce charges by about 10% when using military brass due to reduced case capacity.) Regardless, firing .308 in a loose 7.62x51mm chamber is exactly like shooting it in a sporting rifle with too much headspace.

    That being said, the headspace situation of a rifle ostensibly chambered in 7.62x51mm should be taken on a case-by-case basis. I have an Ishapore Enfield whose headspace is 1.634", or right at NO-GO for .308. It's well below the field reject length for .308, so one could get away with shooting commercial ammo in it. But I prefer to hedge my bets when dealing with 60,000 PSI detonations.

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