Of the couple of dozen or so kaboom accounts I have read over the last couple of years it seems like neither the shooter or bystanders get serious injuries. Contrast this with bolt action rifle failures or others like the M1, M1A, M14, et cetera where failures always cause facial burns and injuries from fragments, sometimes the injuries are very serious. I have always thought this is one of the admirable characteristics of the AR, the ability to protect the shooter in a failure.
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