Colorado’s top law enforcement official on Monday joined a coalition of attorneys general advocating for a federal law that would require background checks for ammunition purchases. Colorado Attorney General Phil Weiser signed a letter to congressional leaders along with 20 other attorneys general in support of Jamie’s Law, a bill that would extend regulations about who can buy guns to those purchasing ammunition. “Existing federal law has too many loopholes that can be exploited by individuals who are prohibited from owning firearms,” Josh Shapiro, attorney general of Pennsylvania, wrote in a letter on behalf of the group.