HARTFORD, CONN. — It’s been a decade since the Wadsworth Atheneum had an exhibit on native son Samuel Colt, an icon who revolutionized the American firearms industry and put Hartford on the world map.

The sign at the door of the Colt factory displays a gun with a slash through it: “No loaded or unauthorized firearms beyond this point.” Understandable for workers at a plant, but also a bit ironic, ...