.223 vs. 5.56 cal ar-15's?

[RM]

About what percentage of ar-15's are calibrated in .223 caliber- as opposed to 5.56? Is this caliber chosen mainly for better accuracy? And if you shoot a 5.56 bullet from a .223 chamber, do you get a ka-boom? You guys are great, thank you!

 

[84B20]

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