They'll file a warrant for your arrest and grab you outside when you don't (like a routine traffic stop) expect it, THEN, they'll go raid your house, and take your guns. One by one I'm sure as nobody will stand up unless its a full on assault.
"offense is the best defense, in call of duty"
It's a federal bill, and a federal registration. You think your local cops are gonna be the raiders? I'm guessing it'll be military, atf or fbi.