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A full metal jacket (FMJ)
A full metal jacket (FMJ) bullet
A bullet is a kinetic projectile, a component of firearm ammunition that is shot from a gun barrel. They are made of a variety of materials, such as copper, lead, steel, polymer, rubber and even wax; and are made in various shapes and constru ...
is a small-arms projectile consisting of a soft core (often lead
Lead () is a chemical element; it has Chemical symbol, symbol Pb (from Latin ) and atomic number 82. It is a Heavy metal (elements), heavy metal that is density, denser than most common materials. Lead is Mohs scale, soft and Ductility, malleabl ...
) encased in an outer shell ("jacket") of harder metal, such as gilding metal
Gilding metal is a form of brass (an alloy of copper and zinc) with a much higher copper content than zinc content. Exact figures range from 95% copper and 5% zinc to “8 parts copper to 1 of zinc” (11% zinc) in British Army Dress Regulations.
...
, cupronickel
Cupronickel or copper–nickel (CuNi) is an alloy of copper with nickel, usually along with small quantities of other metals added for strength, such as iron and manganese. The copper content typically varies from 60 to 90 percent. ( Monel is a n ...
, or, less commonly, a steel
Steel is an alloy of iron and carbon that demonstrates improved mechanical properties compared to the pure form of iron. Due to steel's high Young's modulus, elastic modulus, Yield (engineering), yield strength, Fracture, fracture strength a ...
alloy. A bullet jacket usually allows higher muzzle velocities than bare lead without depositing significant amounts of metal in the bore. It also prevents damage to bores from hard steel or armor-piercing
Armour-piercing ammunition (AP) is a type of projectile designed to penetrate armour protection, most often including naval armour, body armour, and vehicle armour.
The first, major application of armour-piercing projectiles was to defeat the ...
core materials.
History
Despite a widespread belief that the full metal jacket bullet was invented ca. 1882 by Swiss Colonel Eduard Rubin while he was working for the Swiss Federal Ammunition Factory and Research Center, in fact it was known already in the 1880s that the actual inventor was Prussian Major (later Lt.-Col.) (1835-1885), who came up with the idea either in 1875 or 1876. 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. That also allowed bullets to withstand much higher velocities caused by the decrease of the caliber. 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.Impact characteristics
By design, fully jacketed projectiles have less capacity to expand after contact with the target than a hollow-point projectile or a soft-point projectile. While this can be an advantage when engaging targets behind cover, it can also be a disadvantage as an FMJ bullet may pierce completely through a target, leading to less severe wounding, and possibly failing to disable the target. Furthermore, a projectile that goes completely through a target can cause unintentional damage behind the target.See also
* Total metal jacketReferences
External links
* * * {{Handloading Bullets