308 vs 7.62x51. 308 extracts fine, 7.62 will not
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Thread: 308 vs 7.62x51. 308 extracts fine, 7.62 will not

  1. #1
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    308 vs 7.62x51. 308 extracts fine, 7.62 will not

    I have a M&P 10. website and manual states use of 308 and 7.62 can be used. Weapon will fire and extract the 308, but will fire and not extract the fired 7.62. What gives?

    Thanks

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    dj,

    Factory ammo?

    Mike

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    7.62 is not exactly the same as a .308. It seems odd because guns chambered for .308 are well suited to the 7.62 cartridge normally.

    I found this on the web and thought it might come in handy when we start discussign the differences between them.

    So, before we go much further, lets address the oft-posed question "Are the .308 Winchester and 7.62x51 NATO one and the same?"
    The simple answer is no.
    There are differences in chamber specs and maximum pressures. The SAMMI/CIP maximum pressure for the .308 Win cartridge is 62,000 psi, while the 7.62x51 max is 50,000 psi.
    Also, the headspace is slightly different.
    The .308 Win "Go Gauge" is 1.630" vs. 1.635" for the 7.62x51.
    The .308's "No-Go" dimension is 1.634" vs. 1.6405" for a 7.62x51 "No Go" gauge.
    That said, it is normally fine to shoot quality 7.62x51 NATO ammo in a gun chambered for the .308 Winchester (though not all NATO ammo is identical).
    Clint McKee of Fulton Armory notes: "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." You CAN encounter problems going the other way, however. A commercial .308 Win round can exceed the max rated pressure for the 7.62x51. So, you should avoid putting full-power .308 Win rounds into military surplus rifles that have been designed for 50,000 psi max.....
    Reloaders should also note that military ammo often is made with a thicker web. Consequently the case capacity of 7.62x51 brass is usually less than that of commercial .308 brass. You may need to reduce recommended .308 Winchester loads by as much as 2 full grains, if you reload with military 7.62x51 brass, such as Lake City or IMI.
    It really doesn't make much sense unless the brass isn't smooth, or the chamber has some buildup in it. Let's see if the members here can help figure this out.

    Regards,
    Gearchecker
    Last edited by gearchecker; 04-07-2013 at 07:45 PM.
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    Gregory's post about covered it. Military Brass in both 7.62x51 & 5.56x45 are slightly thicker and chambers slightly larger. The logic is thicker brass is less likely to split & the slightly larger chambers also are less likely to gum up in battlefield conditions. Many of the better rifle companies (Browning in particular) make their chambers tight for better accuracy & recommend only commercial ammo. Your chamber could be reamed slightly to accept military ammo but accuracy might suffer, however it should already accept 7.62x51. Either the chamber is slightly too short or needs a serious scrubbing.
    mmitch, s&wtoter, bearcat6 and 2 others like this.
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    I've had similar issues. Actually a variety of feed and extraction issues after firing appx 100 rds of both 308 and 7.62x51. Due to the supply and demand of ammo here in Ohio, I've been at the mercy of whatever is available. So far, I can tell you that match grade and premium 308 feeds and extracts with no problem. The other random 308 and 7.62 I've bought had sporadic problems. Also, the stock mag sold with the this rifle is garbage. I finally got my hands on a Pmag and some PMC 308 and plan to put at least 100 rds through this weekend... We'll see if it has anymore problems.

    Quote Originally Posted by djandnic View Post
    I have a M&P 10. website and manual states use of 308 and 7.62 can be used. Weapon will fire and extract the 308, but will fire and not extract the fired 7.62. What gives?

    Thanks

  7. #6
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    Does it fail to extract with all 7.62x51 NATO or just one kind? I have a box of bad 7.62 that did not get extracted from a Saiga chamber without a stomp on the op handle.

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    JB Bore Paste heavy on a patch wrapped around a chamber brush, chucked up in a drill, will polish the chamber enough any chamber roughness should be removed.
    Don't stick the brush in so deep you will wear the throat. The straight walls of the chamber are what you need to work on.

    And again, it could be the ammo you were using. Not that anyone can be particular these days.....

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    Gearchecker has it right. The .308 Winchester versus the 7.62 x 51mm is just the opposite as the .223 Remington and the 5.56 x 45mm.......in how they operate anyways. There might not be enough "Ooomph" for your gun to cycle the NATO rounds. Crazy that they have to have stuff like this huh?
    I would rather die on my feet, than to live on my knees.

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    .308 vs. 7.62 NATO

    Hi
    I have had good luck with both and also bad luck with both and had a Military person tell me it was the grs. Of bullet I was shooting he said shoot 168grs. Or less as I was shooting the 180 grs. So I purchased just 150 grs. Or less and I am still having issues with the ejection of the case, the rifle shoots it fine but won't always eject and chamber the next round? So I am stumped??? Anyone have any other suggestions?

    Thanks ahead

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    Sierra Match 168Gr STK # 2200 or 175Gr STK # 2275 in a Bolt Gun or Gas Gun. I'm still using 1963 7.62MM Match XM 118 bullet 173grs MV 2550 FPS. Currently I use R15 powder and Winchester LR primers with the previously bullet Sierra bullets. The standard military bullet configuration FMJ weight 150grs. That may have changed from my day.


 
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