An alarm went off one night at Potowmack Elementary School in Sterling, and a surveillance camera recorded the scene: five intruders in masks and hoods darting through hallways and corridors, their assault rifles pointed. In minutes, sheriff's deputies arrived, their own guns loaded and drawn. Only after the gunmen were taken into custody did deputies discover that the assault rifles were replicas — so-called "airsoft" guns that shoot lightweight plastic BBs — and... (GunPolicy.org)