States and cities are taking the lead on bump stock bans

In the immediate aftermath of the deadliest mass shooting in modern U.S. history, there was a fevered pitch to ban bump stocks, the device that allowed the shooter's semi-automatic rifles to mimic the rapid fire of machine guns.

With that push stalled at the federal level, a handful of states and some cities are moving ahead with bans of their own.

Massachusetts and New Jersey — two states at the...