Gun rights advocates say they have filed a federal lawsuit, challenging a new Colorado law banning unserialized guns, which are also known as ghost guns.
"It is appalling to me that people who call themselves American will send death threats to their fellow Americans because of their political views." James T Watson, Highlands Ranch
Last year's Supreme Court decision in a New York case changed a test lower courts had used for evaluating challenges to gun laws, threatening to upend firearms restrictions across the country.