[soapbox] I seriously hope you're not considering using an AR for home defense.   
Or...if you are, I hope that you don't live in any sort of Townhouse/Row House neighborhood, or a single family neighborhood where the houses are close together. 
Even slowed down ALOT, 5.56MM will still penetrate sheet rock like a hot knife through butter, and I'm sure you'd rather not drill one of your neighbors accidentally. [/soapbox]  
 Come on now, Chowser's a cop. I think he knows better.