FMJ (Full Metal Jacket)
Also known as: ball ammo
A bullet with a soft lead core fully encased in a harder metal jacket — inexpensive, reliable target and practice ammunition.
Full metal jacket ammunition wraps a soft lead core in a copper-alloy jacket that covers the nose and sides. The jacket keeps the bore cleaner, feeds reliably in semi-autos, and holds up to higher velocities. FMJ is the cheapest centerfire ammo to shoot, which makes it the standard choice for range practice, training, and competition.
Because FMJ tends to penetrate deeply without expanding, it's generally a poor choice for self-defense — it can over-penetrate a target and pose a risk beyond it. For defensive carry, most shooters choose jacketed hollow points instead, and reserve FMJ for practice.