 The use of full metal jacketing in military ammunition came about in part because of the need for improved feeding characteristics in small arms that used internal mechanical manipulation of the cartridge in order to chamber rounds as opposed to externally hand-reloading single-shot firearms.The harder metal used in bullet jackets was less prone to deformation than softer exposed lead, which improved feeding.It is sometimes thought that military use of FMJ ammunition was the result of The Hague Convention of 1899, Declaration III, prohibiting the use in international warfare of bullets that easily expand or flatten in the body.