How to Read an Ammo Box: Every Number Explained
June 18, 2026 · AmmoBin.com
An ammo box is covered in numbers and abbreviations. Once you know what each means, you can pick the right box with confidence. Here's the decoder.
The key fields
- Caliber — e.g. '9mm Luger', '5.56 NATO' (must match your firearm; see our comparisons)
- Grain (gr) — bullet weight (see our grain guide)
- Bullet type — FMJ, JHP, SP, TMJ, etc. (practice vs defense vs hunting)
- Velocity (fps) — muzzle speed; higher = flatter, more recoil
- Round count — how many rounds in the box (50, 20, 1000…)
- +P / +P+ — higher pressure; only use if your gun is rated for it
Putting it together
'9mm Luger 115gr FMJ 50rd' = fifty practice rounds of standard 9mm. '5.56 62gr JHP 20rd +P' = twenty higher-pressure defensive rifle rounds. See grain explained and FMJ vs JHP to go deeper.
Match every field to your firearm and purpose, then compare cost per round. See live 9mm prices.
Frequently asked questions
What do the numbers on an ammo box mean?
Caliber (what fits your gun), grain (bullet weight), bullet type (FMJ/JHP/etc.), velocity in fps, round count, and any +P pressure rating.
What does 115gr FMJ 50rd mean?
A 115-grain full-metal-jacket bullet (practice ammo), fifty rounds in the box.
Compare live prices