“The Obama administration is considering banning a type of ammunition used in one of the most popular types of rifles because it says the bullets can pierce a police officer’s protective vest when fired from a handgun. The Bureau of Alcohol, Tobacco, Firearms and Explosives is proposing the ban of some types of 5.56 mm rounds — or .223-caliber — used in widely available and popular AR-15-style rifles because the bullets can also be used in some new types of handguns. Other types of 5.56 mm rounds would still be legal to buy, own and fire from guns.”
Source: U.S. considers banning type of popular rifle ammunition