How to Read a Headstamp: Decode Any Cartridge in 30 Seconds
Table of Contents
🎯 What You'll Learn
- What every marking on the bottom of a cartridge means
- Caliber designation, manufacturer codes, and date stamps decoded
- NATO cross symbol, +P markings, and lot numbers explained
- How to identify unknown ammo you find in a can or inherited collection
- Military vs commercial headstamp differences
Every cartridge has a story stamped into its base. The headstamp — the markings on the bottom of a cartridge case — tells you the caliber, the manufacturer, and sometimes the year it was made. Learning to read headstamps takes about five minutes and is one of the most practical firearms skills nobody teaches.
This matters because: you will encounter unmarked ammo. Inherited collections, bulk cans from gun shows, ammo someone handed you at the range — if you can read the headstamp, you can identify exactly what you're holding. If you can't, you're guessing. And guessing about ammunition caliber is how people destroy guns and injure themselves.
The Basic Layout
A typical commercial headstamp contains two to three pieces of information arranged around the primer pocket:
Caliber designation: Usually at the 12 o'clock or 6 o'clock position. Examples: "9mm LUGER", ".45 AUTO", "5.56×45", ".308 WIN", ".223 REM". This tells you exactly what cartridge you're holding. If nothing else, read this.
Manufacturer code: Usually at the 6 o'clock or 3/9 o'clock position. Common codes include FC (Federal Cartridge), WIN (Winchester), RP (Remington-Peters), SPEER, HORN (Hornady), CCI, PMC, S&B (Sellier & Bellot), PPU (Prvi Partizan), MAGTECH, GFL (Fiocchi), TUL (Tula).
+P marking: If present, indicates the cartridge is loaded to higher-than-standard pressure. Usually stamped as "+P" or "+P+" directly on the headstamp. This is a critical safety identifier — +P ammunition should only be used in firearms rated for it.
Military Headstamps
Military ammunition headstamps follow different conventions than commercial. Instead of brand names and caliber designations, military headstamps typically show:
Factory code: A number or letter code identifying the arsenal or contractor. Common U.S. codes include LC (Lake City Army Ammunition Plant), WCC (Western Cartridge Company/Olin), TW (Twin Cities Arsenal), and FC (Federal for military contracts).
Year of manufacture: A two-digit or four-digit year stamp. "LC 22" means Lake City, manufactured in 2022. This is critical for assessing the age and condition of surplus ammo.
NATO cross: A circle with a cross (+) inside it indicates the ammunition meets NATO STANAG specifications. If you see this symbol on a 5.56mm or 7.62mm cartridge, it was manufactured to military pressure and dimensional standards. It's safe in any NATO-spec chamber.
Quick ID: The Most Common Headstamps You'll See
FC 9mm LUGER = Federal, 9mm. WIN .45 AUTO = Winchester, .45 ACP. LC 22 = Lake City military, 2022 production. S&B 9×19 = Sellier & Bellot, 9mm (European designation). PPU .308 WIN = Prvi Partizan (Serbian), .308 Winchester. TUL 223 REM = Tula (Russian), .223 Remington steel case.
Identifying Unknown Ammo
You inherited grandpa's ammo can. There are loose rounds mixed together. Here's the process:
Step 1: Read the headstamp. Caliber designation is your starting point. If it says "30-06 SPRG" or ".308 WIN", you know what you have.
Step 2: No readable caliber? Measure the cartridge. Overall length, case length, bullet diameter, and rim diameter will identify any cartridge when cross-referenced with a reloading manual or online cartridge database.
Step 3: Check condition. Look for corrosion (green/white residue on brass), dents in the case, set-back bullets (bullets pushed deeper than normal into the case), or loose primers. Damaged ammo should be disposed of — most local ranges and gun shops have ammo disposal programs.
Step 4: Unknown headstamps. If the markings are unfamiliar, photograph the headstamp and search online. Dedicated databases like cartridgecollectors.org and head-stamp.com catalog thousands of military and commercial headstamp patterns with full identification.
When in Doubt, Don't Shoot It
If you cannot positively identify a cartridge's caliber, do not attempt to fire it in any firearm. A wrong-caliber round can cause catastrophic failure. Take unknown ammunition to a knowledgeable gun shop or range officer for identification. It's free and it might save your hands.
Rimfire Headstamps
Rimfire cartridges (.22 LR, .22 WMR, .17 HMR) have simpler headstamps — usually just a manufacturer code. Common .22 LR headstamps: U (Remington), F (Federal), C (CCI), W (Winchester), A (Aguila). The caliber is usually NOT stamped on rimfire headstamps because the cartridge dimensions are obvious to anyone who handles them regularly.
The important rimfire distinction: .22 LR and .22 WMR are different cartridges. .22 WMR (Winchester Magnum Rimfire) is wider in diameter and longer than .22 LR. They are NOT interchangeable. If a headstamp on a small rimfire cartridge is unfamiliar, measure before shooting.
FAQ
Does headstamp date affect reliability?
What does "NATO" on a headstamp mean?
Can I reload brass with military crimped primers?
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