Full metal jacket (ammunition)

A bullet jacket usually allows higher muzzle velocities than bare lead without depositing significant amounts of metal in the bore.

[5][6][7][8][9] 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.

[10] In addition to the various advantages afforded by FMJ rounds, the Hague Convention of 1899, Declaration III, prohibits the use in international warfare of bullets that easily expand or flatten in the body.

Unjacketed lead bullets readily expand on impact, effectively mandating FMJ by international law.

These .30-caliber (7.62 mm) full metal jacket bullets show the typical jacket openings exposing the lead alloy core on the base of the bullet to illustrate that a full metal jacket may not completely enclose the core.
Examples of FMJ bullets in their usual shapes: pointed (" spitzer ") loaded in the 7.62×39mm rifle and round-nosed loaded in the 7.62×25mm pistol cartridges