A federal jury has convicted a small-town Iowa police chief of lying to federal authorities to acquire machine guns. Prosecutors say he sold the guns for his own profit.

These small pieces modify guns for rapid-fire and are classified as machine guns themselves. As the $2,500 printers showed, hobbyists and criminals can easily exploit rapidly improving technology.

In New Mexico, police and prosecutors backed an effort to outlaw devices that convert pistols into machine guns. In Alabama, the governor made it a priority. Lawmakers in both states — one led ...