The AR-15 has become the mass-casualty murderer's weapon of choice, most recently in San Bernardino. It's possible, of course, that Remington executives just got lucky about their gun getting famous — or learned from the tobacco industry and committed nothing at all to paper. But a decade without public scrutiny can also make people say more than they should about how the terrible acts they know their merchandise makes all but inevitable, and the sales surge that often follows those attacks.