Full metal jacket bullet

For the Stanley Kubrick film, see Full Metal Jacket.

An example of FMJ bullets in their usual shapes: pointed ("spitzer") for the 7.62x39mm rifle and round-nosed for the 7.62x25mm pistol cartridges.

A full metal jacket (or FMJ) is a bullet consisting of a soft core (usually made of lead) encased in a shell of harder metal, such as gilding metal, cupronickel or less commonly a steel alloy. An FMJ bullet is encased only on the front and sides, leaving the bottom as bare lead. Total metal jacket (TMJ) or complete metal jacket (CMJ) bullets are totally encased.

Totally encased bullets are not subject to exposing the bullet base to high-temperature gasses when the bullet is fired, thereby reducing the lead vapor generated. Thus TMJ and CMJ bullets are better suited for indoor firing ranges. The British overcame this by including a disc of fibreboard, similar to printed circuit board, over the top of the cordite charge and under the projectile of the .303 British ammunition. This also provide a rudimentary scraping or cleaning off residues in the barrel each time a shot was discharged.

The use of full metal jacketing came as a result of the The Hague Convention of 1899, Declaration III, prohibited the use in international warfare of bullets that easily expand or flatten in the body.

However, many states ban the use of non-mushrooming ammunition for hunting, since it is more likely to wound instead of kill.^[1]

In general, a bullet jacket allows for higher muzzle velocities than bare lead without depositing significant amounts of metal in the bore. It also prevents damage to bores from steel or armor-piercing core materials. The appearance of jacketed ammunition is highly distinctive when compared to hollow-point or soft point bullets. Historically, the first successful full metal jacket rifle bullets were invented by Lt. Col. Eduard Rubin of the Swiss Army in 1882.^[2]^[3]^[4]^[5] Full metal jacket bullets were first used as standard ammunition in 1886, for the French Mle 1886 Lebel rifle.

Disadvantages

There are some disadvantages to jacketing a bullet.^[6] For instance, full metal jacket bullets have different behavioural properties, both inside the barrel of the gun and also in flight. Whereas hollow point and soft-tipped bullets are designed to expand upon impact, metal jacketed bullets have a very limited capacity to expand. This generally makes the bullet pierce through a soft target, often leading to less severe wounding, and possibly failing to disable the target. Hollow point and soft tipped bullets are for use against soft targets only, such as animals or people, whereas full metal jacketed bullets can be used effectively against both soft and hard targets.

FMJ with variable cores

Some designs of FMJ rifle ammunition inflict more destructive gunshot wounds than others. Not all FMJ bullets contain a simple lead filling. Here are some examples:

Although British Mark 7 .303 ammunition is compliant with the terms of the Hague Convention, it creates more destructive gunshot wounds than standard spitzer bullets due to its internal design. The center of gravity of the Mark 7 bullet is deliberately shifted towards the rear. This is achieved by constructing the front third of the interior of the bullet from a lighter material such as aluminum or wood pulp or, as was done in Australia to save on scant materials, Bakelite. The use of Bakelite also satisfied British requirements where if wood pulp was used, it would have to be autoclaved. The result is a tail-heavy FMJ bullet which yaws violently after hitting the target. The .303 British Mark 7 ammunition has been replaced by the 7.62x51mm NATO. Most 5.45x39mm FMJ ammunition is made with an air space in the tip of the round similarly shifting the weight to the rear causing immediate and violent tumbling when it contacts a soft target. 5.56x45mm NATO ammunition traveling at the proper velocity will also tumble and the round will break apart at the cannelure and fragment.