5.56/.223


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Old 07-03-2009, 03:20 PM   #1
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Default 5.56/.223

So every time we go and have some fun with the AR's someone ALWAYS! brings up the question, " hey so... if a 5.56 can shoot .223 with no problem why is it advised not to shoot 5.56 with a .223" There is always the person that chimes in "It can .223 and 5.56 are the exact same thing except 5.56 is military ammo and .223 is the civilian ammo". But yet even the people saying there both the same will not load a 5.56 into there .223.

So whats the truth...?



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Old 07-03-2009, 03:24 PM   #2
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There are some small subtle differences in the case measurements between the two. There is also a large difference in the SAAMI specs on case pressure, which is the important difference.



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Old 07-03-2009, 03:39 PM   #3
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Good question, i've wondered the same thing myself.

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Old 07-03-2009, 04:05 PM   #4
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From Wikipedia:

While the external case dimensions are very similar, the .223 Remington and 5.56x45mm differ in both maximum pressure and chamber shape. The maximum and mean pressures for some varieties of the 5.56 mm (different cartridge designations have different standards) exceed the SAAMI maximums for the .223 Remington, and the methods for measuring pressures differ between NATO and SAAMI.[2] The 5.56 mm chamber specification has also changed over time since its adoption, as the current military loading (NATO SS-109 or US M855) uses longer, heavier bullets than the original loading did. This has resulted in a lengthening of the throat in the 5.56 mm chamber. Thus, while .223 Remington ammunition can be safely fired in a 5.56 mm chambered gun, firing 5.56 mm ammunition in a .223 Remington chamber may produce pressures in excess of even the 5.56 mm specifications due to the shorter throat.[3]

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