The Bureau of Alcohol, Tobacco, Firearms and Explosives on Thursday raised new concerns about surplus military ammo used in popular AR-15 rifles and pistols just days after pulling back on a proposal to ban the ammo because it could threaten police safety.

In a Senate Appropriations Committee hearing, ATF Director B. Todd Jones said all types of the 5.56 military-style ammo used by shooters pose a threat to police as more people buy the AR-15-style pistols.