.223 vs 5.56

Discussion in 'AR-15 Discussion' started by truckie98, Oct 20, 2012.

  1. truckie98

    truckie98 New Member

    I've been told you can shoot a 223 through a 556 but not vise versa any knowledge about this out there?
  2. Vincine

    Vincine New Member

    I looked into this. There are extensive threads on FTF, which I have contributed to, in the ammo sub-forum I believe, and elsewhere concerning this.

    The gist of it is there are small differences in the neck/throat area of the cartridges and corresponding chambers that result in higher pressures in a military 5.56. It was adopted from the civilian 223, but I believe it was changed to provide more energy in order to reliably cycle a dirty automatic weapon under adverse conditions, which a bolt action .223 didn't need to do.

    You can shoot a 5.56 out of a .223 firearm but it’s supposed to fatigue the weapon over time and may prove dangerous. I don’t know how many rounds that would take. There are others who load ‘hot’ 223s and use them without issue, so I don’t know whether this is just a theory or a proven fact.

    You can shoot a .223 out of a 5.56 without any problem, but may suffer a slight accuracy loss. That said, I would think the difference would be way smaller that one’s own inconsistency in marksmanship.

    Rock River Arms’ AR15s, and some others, use a ‘Wylde’ (sp?) Chamber’ which is designed to shoot either without any difference in fatigue or accuracy.

    Mossberg makes a bolt action that’s chambered for 5.56. I don’t know of any others. It seems to be rare relatively speaking. You would think there would be more given the flexibility of ammunition a ‘dual' .223/5.56 chambered weapon could use.

    And if I wrong I’m sure someone here will let us know straight away.
    Last edited: Oct 20, 2012

  3. alsaqr

    alsaqr Well-Known Member Supporter

    SAAMI has been spewing this stuff since large quantities of 5.56mm surplus ammo came on the market: Before that SAAMI was silent on the issue. I've been firing 5.56mm M193 US ammo in my .223 rifles since 1968. The fifteen or so .223 rifles i have owned since 1968 have fired at least 200,000-250,000 rounds of 5.56mm ammo with no ill effects. If you don't feel comfortable firing 5.56mm ammo in your .223 then don't do it.

    Until recently no one had tested this SAAMI claim. That has now changed:


    There are at least one dozen different .223/5.56mm chambers. Here are some of them. See detailed reamer dimensions:

    Last edited: Oct 20, 2012
  4. Vincine

    Vincine New Member

    Wow! Science!

    It always seemed to me that tests with consistent pressure measurement methodology would have been easy enough to perform. I couldn’t understand why it was never done, until now. It also seemed to me that what differences in pressure there are, should have been easily accommodated by the safety tolerances engineered into the product. I was surprised that firing a 5.56 in a .223 barrel was considered a risk. I would’ve expected the .223 barrels, or any firearm for that matter, would be much more robust and be able to handle pressures two or three times the stress.

    Thanks for this.