question on 5.56 and .223

Discussion in 'Black Rifle Forum' started by Phantom465, Mar 23, 2013.

  1. From the info I have Googled, 5.56 and .223 are virtually the same size, but 5.56 usually has higher pressure. Is that correct?

    With that in mind, what parts really matter when it comes to higher presser. Certainly the barrel needs to be rated for higher pressure. What are parts should I be concerned about?


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  3. flw


    Rifle made for 556 will shoot 223 as well but not the other way around. 223 rifle will not shoot 556. There is a difference in the dimensions. You need to look at more than the caliber

  4. Not exactly. A rifle chambered in .223 WILL chamber and fire a 5.56 cartridge, but it can result in an unsafe over-pressure situation that can damage the weapon and even possibly harm the shooter.

    OP: The chamber needs to be a 5.56 chamber, or .223 Wlyde (A match chamber specifically designed to handle 5.56 ammo). If you are specifically looking at AR-15s, it has been a LONG time since I saw one that did not have one of those two chambers cut into the barrel.

    Also, it's the marking on the BARREL that matter, not what's on the lower.
    #3 WoodenPlank, Mar 23, 2013
    Last edited: Mar 23, 2013
  5. Thanks - I am building an AR from the ground up. Are there any other parts that I should be concerned about? What about the bolt / bolt carrier or upper receiver?
  6. ked


    i understand about the 5.56 or .223 wylde chamber, but can you be more specific about what exactly causes the excessive pressure?

    thanks, ked
  7. Upper receiver doesn't matter, so long as it made to spec (ie: caliber doesn't matter, just has to be an AR-15 upper receiver). So long as the bolt is made for .223/5.56 (no difference between them for the bolt), and is from a quality manufacturer, you'll be fine. I am partial to Bravo Company, Daniel Defense, and LMT bolts (in that order, usually - consequently, that seems to be the order of availability).

    For reliability, the two most critical parts are the barrel and bolt carrier group. As long as you buy quality on those, you should be fine. Accuracy will vary between individual builds, so the only way to know how accurate YOUR rifle will be is to get out and shoot it.

    A standard .223 chamber has a shorter leade than .223 Wylde or 5.56. Also, 5.56 cases have slightly smaller internal dimensions due to thicker case walls. Those two factors (tighter chamber and tighter internal case dimensions) contribute to higher chamber pressures. Bear in mind that this is all in GENERAL terms, as the exact dimensions can vary between production runs and manufacturers - sometimes dramatically.

    Lucky gunner labs had a great write-up on the two a while back, and it's worth reading.

    Their conclusion was that, while shooting 5.56 from a .223 chamber isn't likely to turn your gun into a bomb (although it CAN happen in certain situations), it can potentially cause some issues - popped primers, or greater wear over time.

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