When goods can't cross borders, ideas will. Also 3-D printer files:
UK police seize parts from 3D-printed gun.
...Apparently a trigger and a magazine. Last time I looked, you didn't need either one of of those to make a gun (see zip gun, fire lance, handgonne). ...Hey, actual Bad Guys in possession of actual Means To Do Harm is a bad thing, but let's make sure we can tell baddies from posers and the "means" from toys.
Bonus: in the body of the story, AP serves up the "invisible to metal detectors" canard. Drink! (Also, call me back when J. Random Hijacker manages to get the bullets through a metal detector.)
You can't unring a bell.
Update, via Jed and Bear in comments: Or not even gun parts at all. Or a gang member.
Associated Press, straining at gnats and swallowing camels whole, especially where firearms are involved; Agence France-Presse, skeptically methodical; J. Random Police Constable, UK edition: hysterical. In both senses.
4 weeks ago