SEATTLE — Lawmakers around the country are making a renewed push to ban high-capacity magazines that gunmen have used in many recent massacres, allowing them to inflict mass casualties at a startling rate before police can stop the carnage. Nine states have passed laws restricting magazine capacity to 10 to 15 bullets, and the Democratic-led U.S. House plans to consider a similar ban at the federal level in the coming weeks. In arguing for the bans, politicians, experts and gun-control advocates point out that in the time it takes for a driver to wait through a stop light, a shooter...