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.223 -vs 5.56 Firing Pin

Discussion in 'Rifle Country' started by OhioChief, Sep 26, 2011.

  1. OhioChief

    OhioChief New Member

    I never realized before that the firing pin is different between the .223 and the 5.56. Anybody know why this is? What happens if you swap them?
  2. mortablunt

    mortablunt New Member

    It is because they are slightly different calibers. Also, the 5.56 round for the military generates higher pressure and therefore, the plumbing must be stronger. You can use .223 in a 5.56, but you cannot use a 5.56 in a .223.
  3. 303tom

    303tom member

    Biggest Myth Ever !!!!!!!!!!!!!
  4. Sediment

    Sediment New Member

    5.56 NATO is a Military round with a "Military Primer" meaning that it's harder. Firing pin is probably made of a harder or heavier metal.

    AFAIK though there shouldn't be a difference in firing pins is you are running a bolt carrier for a gun in .223 Rem or 5.56 NATO.
  5. W.E.G.

    W.E.G. Active Member

    WHAT are you talking about?

    Who told you this?
  6. 68wj

    68wj New Member

    X2. Never heard that. I use an AR-15 FP in my AR's, not a cartridge specific part.
  7. Bartholomew Roberts

    Bartholomew Roberts Moderator Emeritus

    The only difference I have ever noticed is that some (though by no means all) manufacturers make the firing pin collar on their "AR15" firing pins bigger in order trap the hammer if the disconnector fails.
  8. MtnCreek

    MtnCreek Active Member

    How does this work? I thought the hammer would fall foward of the bolt/carrier when the disconnector failed.
  9. bigedp51

    bigedp51 member

    The .223 and the military 5.56 Nato are the same cartridge, if you look at CIP the European equivalent of the American SAAMI you will see CIP considers these cartridges to be the same. (along with the .308 and 7.62 NATO)

    The pressure myth started when the pressure readings were changed from CUP to the transducer PSI method and exacerbated when our military changed to NATO EPVAT testing where the chamber pressure is measured at the neck of the case which reads even higher.

    The only difference between the "older" .223 rifles and the 5.56 is the rate of twist and the throat of the chamber of the "newer" M16/A4 rifles. My Stevens 200 has a 1 in 9 twist, the same as the "newer" M16/A4 rifles and my firing pin is no different. Military ammunition stakes or crimps its primers to keep the primer from backing out of the primer pocket at the longer headspace settings of military small arms.

    Before these Internet myths started you never heard someone saying the military 30-06 was a different cartridge from the civilian commercial 30-06. I think I'll start a new rumor, my 03 had a gold plated firing pin and was made from Fairy dust.
  10. Carl N. Brown

    Carl N. Brown Active Member

    Generally, 5.56 barrel chambers will be throated for longer heavier bullets than most .223 commercial ammo.

    Generally though you really ought to check with the manufacturer, because some barrels marked .223 are actually chambered to accept 5.56 as well as .223, while most .223 barrels especially older .223 barrels are chambered for the shorter, lighter bullets originally loaded in commercial .223 ammo.

    I suspect that the only difference in firing pins is between early ARs that were semi-auto versions of the M16, and current ARs designed as semi-auto from the get-go.
  11. dprice3844444

    dprice3844444 member

    what are these guys smoking? and they didn't offer me none?
  12. MtnCreek

    MtnCreek Active Member

    When did they start using 1:9 and what was the stated reason?
  13. 303tom

    303tom member

    I do know that the 7.62x63 run a higher pressure than the .30-06 does !
  14. Jenrick

    Jenrick Active Member

    The M16 family since the A2 have a 1/7" barrel twist, not a 1/9".

  15. Bartholomew Roberts

    Bartholomew Roberts Moderator Emeritus


    The animation at that link should show how it works; but basically if the disconnector fails the hammer follows the bolt carrier, as the bolt goes back into battery the notched AR15 style hammer slides up the underside of the unshrouded AR15 style carrier and snags the firing pin collar, causing the rifle to stop functioning.
  16. rcmodel

    rcmodel Member in memoriam

    As others have already said.
    It isn't different.

    In any brand of firearm I can think of that is chambered in both calibers, the part# for all the bolt parts, including the firing pin, is exactly the same.

  17. Bartholomew Roberts

    Bartholomew Roberts Moderator Emeritus

    Here is a picture showing the different diameters in firing pin collars between M&A Parts's AR15 firing pin and M16 firing pin:

    Although I apparently got the details backwards, the M16 firing pin is the one with the larger collar. It is the AR15 firing pin, which has the reduced collar so that the combination of an unshrouded bolt carrier and large collar doesn't cause issues.

    Colt was the original manufacturer who is responsible for this difference. This is why Colt has two different firing pins for the AR15: Firing Pin (Auto) SP62294 (0.374" diameter) and Firing Pin (Semi) SP63039 (0.331" diameter).

    And again, I think most manufacturers just use the smaller collar firing pin in all of their products these days rather than deal with the two different parts. I'm not even sure what the technical advantage of the larger collar would be in a shrouded bolt carrier.
  18. OhioChief

    OhioChief New Member

    Well I heard about it when I was at the gun show and wanted to pick up a few extra firing pins. they asked do I want .223 or 5.56. I said "what's the difference" and they showed me. The head (where the hammer srikes) is about a third the size larger on the 5.56. I went home and compared my own .223 pins with my own 5.56 pins, and sure enough, that's exactly what I had from the manufacture. Just never put them side by side before and noticed the difference.
  19. 68wj

    68wj New Member

    That was an AR-15 versus an M-16 pin. Fortunately, they are interchangeable. Hopefully they had some good beef jerky at that booth too.:p
  20. bigedp51

    bigedp51 member


    Don't get "twisted" out of shape, my mistake and forgetfulness, my quick reference material was the Hornady manual that was the closest to the computer.

    The correct military twist for the M16A4 is 1 in 7. :eek:


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