Before a shooter released a seemingly endless torrent of bullets over a crowd gathered at a concert in Las Vegas earlier this year, most of the country didn’t know what a bump stock was. But it was the tiny attachment that had turned the Las Vegas shooter’s guns into weapons of mass destruction: Stephen Paddock had outfitted at least 12 of his rifles with bump stocks, which, attached to semi-automatic weapons, give them rapid-fire, continuous shooting capabilities. More than 50 people were kille…