Additionally, Heller talks common use for "lawful purposes" is there a more lawful purpose than upholding the law? The more we point to law enforcement effectively, the stronger our argument gets. DHS says a 30 round AR-15 is suitable for personal defense. They're a law enforcement organization. Common use lawful purpose.
Then we point to the "miitia" Korean grocers in the LA riots. The history of posse comitatus, and its origins in hue and cry..