Ammunition 101: Understanding Calibers, Cartridges, and Loads
Understanding ammunition is essential for every gun owner. Whether you're buying your first box of ammo or stocking up at a gun show, this guide covers the fundamentals.
Anatomy of a Cartridge
A modern cartridge has four components:
- Case — The brass, steel, or aluminum shell that holds everything together
- Primer — A small charge at the base that ignites when struck by the firing pin
- Powder — Propellant that burns rapidly to generate expanding gas
- Bullet — The projectile that exits the barrel
The terms "round," "cartridge," and "ammunition" all refer to the complete assembly. "Bullet" technically refers only to the projectile — though it's commonly used interchangeably.
Understanding Caliber
Caliber refers to the diameter of the bullet, and by extension, the specific cartridge designation. Calibers are expressed in two systems:
Imperial (Inches)
- .22 LR — 0.22-inch bullet diameter
- .45 ACP — 0.45-inch bullet diameter
- .308 Winchester — 0.308-inch bullet diameter
Metric (Millimeters)
- 9mm Luger (9x19mm) — 9mm bullet diameter, 19mm case length
- 5.56x45mm NATO — 5.56mm bullet diameter
- 7.62x39mm — The AK-47/SKS cartridge
Common Handgun Calibers
| Caliber | Common Use | Recoil | Cost |
|---|---|---|---|
| .22 LR | Training, plinking | Very low | Very low |
| 9mm | Self-defense, duty | Low-moderate | Low |
| .40 S&W | Self-defense, duty | Moderate | Moderate |
| .45 ACP | Self-defense | Moderate-heavy | Moderate |
| .380 ACP | Pocket carry | Low | Moderate |
| .357 Magnum | Self-defense, hunting | Heavy | Moderate |
| .38 Special | Self-defense, target | Low-moderate | Moderate |
Common Rifle Calibers
| Caliber | Common Use | Recoil | Cost |
|---|---|---|---|
| .22 LR | Training, small game | Very low | Very low |
| 5.56/.223 | AR-15, varmint | Low | Low |
| .308/7.62x51 | Hunting, precision | Moderate | Moderate |
| 7.62x39mm | AK/SKS platform | Moderate | Low |
| .30-06 | Hunting (all game) | Moderate-heavy | Moderate |
| 6.5 Creedmoor | Precision, hunting | Low-moderate | Moderate |
| .300 Win Mag | Long range, big game | Heavy | High |
Types of Ammunition
Full Metal Jacket (FMJ)
A lead core with a copper jacket. Used for target practice and training. Affordable and widely available. Not ideal for self-defense due to over-penetration.
Hollow Point (HP / JHP)
Designed to expand on impact, creating a larger wound channel and reducing over-penetration. The standard choice for self-defense and law enforcement.
Soft Point (SP)
A partially jacketed bullet that expands on impact. Common for hunting — provides controlled expansion and deep penetration.
Frangible
Designed to break apart on impact with hard surfaces. Used for close-range training and home defense where over-penetration is a concern.
Shotgun Loads
- Birdshot — Small pellets for birds and clay targets
- Buckshot — Larger pellets for self-defense and deer hunting
- Slugs — A single large projectile for accuracy at longer range
Buying Ammunition
At Gun Shows
Gun shows are one of the best places to buy ammunition in bulk at competitive prices. You'll find vendors specializing in popular calibers as well as hard-to-find or surplus ammunition. Find a show near you in our show directory.
Online
Online retailers like AmmoSeek, SG Ammo, and Lucky Gunner offer competitive pricing with shipping to your door (check state laws — some states restrict online ammo purchases).
At Gun Shops
Convenient but typically the most expensive option. Use our dealer directory to find shops near you.
Storage Tips
- Store in a cool, dry place — ammunition is shelf-stable for decades when stored properly
- Use ammo cans with desiccant for long-term storage
- Rotate your self-defense ammunition annually
- Keep away from heat, moisture, and solvents