Ammo Dictionary

Complete Guide to Ammunition Terms

If you’re new to firearms or looking to expand your knowledge, understanding ammunition terminology is essential. Below is a comprehensive guide to ammo-related terms, covering everything from bullet types to ballistics and legal considerations.

Ammunition Basics

Bullet: The projectile that is fired from a firearm. Often confused with the entire cartridge.

Cartridge: The complete round of ammunition, which includes the bullet, casing, primer, and gunpowder.

Casing: The shell that holds the components of a cartridge together. Can be made of brass, steel, or aluminum.

Primer: The small component at the base of the cartridge that ignites the gunpowder when struck by the firing pin.

Propellant (Gunpowder): The chemical compound that burns and generates gas to propel the bullet forward.

Bullet Types & Functions

FMJ (Full Metal Jacket): A bullet with a soft lead core encased in a harder metal shell. Ideal for target practice and range shooting.

HP (Hollow Point): A bullet designed with a hollow tip that expands upon impact, increasing stopping power and reducing over-penetration. Preferred for self-defense.

JHP (Jacketed Hollow Point): A hollow point bullet with a metal jacket for better penetration and controlled expansion.

SP (Soft Point): A bullet with an exposed lead tip, offering controlled expansion. Commonly used for hunting.

Ball Ammo: Another term for FMJ ammunition, often used for military-style training.

Tracer Rounds: Ammunition with a pyrotechnic charge that creates a visible streak when fired. Illegal for civilian use in California.

Armor-Piercing (AP): Specialized rounds designed to penetrate body armor. Illegal for civilian use in California.

Ammunition Measurements & Ballistics

Caliber: The internal diameter of a firearm’s barrel, measured in inches (e.g., .45 ACP) or millimeters (e.g., 9mm).

Grain (gr): A unit of weight used to measure bullets and gunpowder. One grain = 1/7,000 of a pound. Heavier grains typically mean more stopping power.

Muzzle Velocity: The speed at which a bullet exits the firearm barrel, measured in feet per second (fps).

Muzzle Energy: The amount of kinetic energy a bullet has when leaving the barrel, measured in foot-pounds (ft-lbs). Higher energy means greater impact force.

Ammo Types by Use Case

Self-Defense Ammo: Typically hollow point rounds designed for maximum stopping power with minimal risk of over-penetration.

Target Ammo: Usually FMJ rounds, designed for affordability and reliability in training and practice sessions.

Hunting Ammo: Can include soft point or hollow point rounds, optimized for controlled expansion and ethical kills.

Subsonic Ammo: Designed to travel below the speed of sound (~1,125 fps) to reduce noise, often used with suppressors.

Shotgun-Specific Terms

Gauge: The size of a shotgun bore. Common gauges include 12 gauge, 20 gauge, and .410 bore. A lower number means a larger diameter.

Buckshot: Large-diameter pellets used for self-defense and hunting.

Birdshot: Smaller pellets used for hunting birds and small game.

Slug: A single, large projectile fired from a shotgun for maximum stopping power.

Specialized Terms

+P (Overpressure Ammunition): A higher-pressure round that offers increased velocity and stopping power. Firearms must be rated for +P to safely use it.

Rimfire vs. Centerfire: Rimfire ammo (e.g., .22LR) has the primer around the case rim, while centerfire ammo has the primer in the center of the base. Centerfire is more powerful and reloadable.

Reloading: The process of assembling ammunition by reusing spent casings with new primers, powder, and bullets.