Many modern sporting rifles and some pistols are built with chrome-lined barrels to increase durability and extend a barrel’s life. In the early days of fielding the M-16 to troops in Vietnam, Colt added a chrome lining to the barrels to increase durability under excessive rates of fire. The heat and pressure from extended use could “shoot out” the rifling on a non-chrome-lined barrel. Since then, many firearms manufacturers now include a chrome lining in their barrels to help them last longer and maintain accuracy over years of use.