User blog comment:JoeRamirez/Call of Duty Modern Warfare 3 Weapons Wishlist./@comment-82.38.219.232-20110706210946/@comment-1715386-20110708135500

I have no idea if the grip is actually from an AR-15 though I do know that H&K actually told the US Army that they only had to buy the upper receiver because it was compatible with the M16's lower receiver. Maybe that's what you're seeing.