Bump stock ruling could trigger booming rapid-fire marketplace

If the Supreme Court rules that bump stocks aren’t machine guns later this summer, it could quickly open an unfettered marketplace of newer, more powerful rapid-fire devices.

The Trump administration, in a rare break from gun rights groups, quickly banned bump stocks after the 2017 mass shooting at a Las Vegas concert that was the deadliest in U.S. history. In the ensuing years, gun rights groups challenged the underlying rationale that bump stocks are effectively machine guns — culminating...