A full metal jacket is a bullet consisting of a soft core 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
or Complete Metal Jacket 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. 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. 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. 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. 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.
Images of FMJ ammunition
See also Soft-point bullet
Hollow-point bullet References
Huon, Jean. Military Rifle and Machine Gun Cartridges. Alexandria, Va.: Ironside International.
ISBN 0-935554-05-X. OCLC 24498827.
External links Declaration concerning Expanding Bullets,
made at the 1899 International Peace Conference at The Hague, which entered into force on
September 4, 1900 European Ammunition Box Translations
Photos showing terminal effects of British Mark 7 .303 bullets