My brother Matt Hanna sent this to me in an email:
Want to buy this DJI Phantom 3 quadcopter?
It’s illegal unless you register it with the federal government.
Want to buy this S&W M&P15 5.56mm NATO caliber carbine?
It’s against federal law to maintain a registry of who has bought it.
And bonus!: It’s cheaper than the DJI Phantom and, according to Wikipedia, can penetrate one side of a steel helmet from 600 meters away!