What’s the Difference Between the .223 vs 5.56?

Written by Sierra Bullets Ballistic Technician Paul Box

Over the last year or so we’ve had hundreds of calls on our 800 line concerning the difference between the .223 and the 5.56. So what is the real difference ?

In reality these two are the exact same cartridge. The case dimensions are the same. The difference is in a combination of throating and how they are loaded. Maximum working pressure for the .223 has been established by SAAMI at 55,000 PSI. Maximum pressure for the 5.56 has been taken up to 60,000 PSI. This was accomplished by using a longer throat in the 5.56. Much in the same way Weatherby has done for years with their long free bore. This longer bullet jump allows for  heavier powder charges and naturally higher pressures.

So is it safe to shoot a 5.56 in a .223? Probably not if that rifle has a common throat length. Pressures could run high enough to blow a primer and etch a bolt face. Smoke boiling out of the action and can get pretty hairy in general. So what’s the safe thing to do ? Use .223 in .223 and 5.56 in 5.56. It will be easier on your nerves.

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9 Responses to What’s the Difference Between the .223 vs 5.56?

  1. firstriverbend says:

    And much easier on your firearm!! 🙂


  2. Chris Bass says:

    For reloading brass purposes… can you use the .223 brass interchangeably with 5.56 brass? (Not factory loads, but handholds.) Provided you work up?


  3. Paul Box says:

    Yelp…..no problem there at all.


    • Chris Bass says:

      I came into a bunch of LC brass recently.


      • firstriverbend says:

        There are two things you need to be aware of, all LC brass will have a crimped primer, so that needs to be removed after you deprime and most LC brass will have a smaller internal volume. That is important because it will cause higher pressures if you do not adjust the powder accordingly.
        But you did say “work up”, which should take care of that problem. 🙂
        I like LC brass myself, but then I like most brass!


  4. Lyle Morton says:

    Paul, How does the 223 Wilde chamber fit in the mix. They sell it for use with either 5.56 or 223. What do you recommend?


  5. Paul Box says:

    The Wide chamber is set up to load an 80 MK to have an OAL OF 2.445″ AND JUST BE TOUCHING THE RIFLING. It will handle standard .223 as well as 5.56 ammo.


  6. Brian Klosterman says:

    What’s the best way but also doing it on the cheap, can on get the primer out of a Lake City Case.
    I have about 300 rounds of Lake City Ammo cases?


  7. Paul Box says:

    Lee makes a little tool just for this. It’s a harden punch and case holder. It will work for you.


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