As a result of the easy availability of armor-piercing bullets, laws banning the sale or possession of them have recently been passed in Alabama, California, Oklahoma, Kansas, Illinois, Minnesota, and Rhode Island. There is little information available on how often criminals have obtained or used armor-piercing handgun bullets, but it appears that deliberate use of such bullets by criminals is extremely rare. Proposed Federal legislation (H.R. 5437) to prohibit the sale or possession of such ammunition defines such ammunition as any bullet that when fired from a gun with a barrel of 5 inches or less will penetrate 18 layers of Kevlar, the material from which most police protective vests are made. The National Rifle Association, the Departments of Treasury and Justice, as well as bullet manufacturers oppose the legislation primarily on the ground that it is too complicated to define armor-piercing ammunition in a law. The proposed law would possibly make it illegal for police officers to carry their own private stocks of armor-piercing ammunition, although police representatives generally support the legislation. Some police survival instructors encourage officers to carry at least a few rounds of armor-piercing ammunition, but not in the holstered gun, since many officers are shot with their own guns.