WASHINGTON (AP) — The Obama administration wants to ban a type of ammunition used for one of the most popular rifles on the market.

The Bureau of Alcohol, Tobacco, Firearms and Explosives is considering banning certain types of 5.56 mm rounds that can pierce a police officer's protective vest when fired from a handgun. It's accepting public input on the idea for two more weeks.

An ATF spokeswoman, Ginger Colbrun, says the ban would only affect "M855 green tip" rounds with certain types of metal cores, including those made of steel, iron or brass. The National Rifle Association is urging its members to write to the agency and members of Congress to object to the proposed ban.