What Is a Cartridge Headstamp? How to Read the Markings on Your Ammo
Turn a round over and you’ll find letters and numbers stamped around the base. That marking is the cartridge headstamp, and it’s the quickest way to check that a round matches your firearm.
This cartridge headstamp guide explains what the markings mean, how to read them and where they stop being useful. It draws on SAAMI’s published standards, a Small Arms Survey research brief and a defense-industry article, and we say which is which.
Last reviewed: October 13, 2026.
The one rule that matters most: the cartridge name on the headstamp or box must match the marking on your firearm. If you have any doubt, don’t fire it.
In This Guide
- Cartridge headstamp: the short answer
- Cartridge headstamp: what the markings mean
- Cartridge headstamp: SAAMI abbreviations
- Cartridge headstamp: how to read one
- Cartridge headstamp: similar names that don’t mix
- Cartridge headstamp: +P markings
- Cartridge headstamp: military and NATO marks
- Cartridge headstamp: rimfire rounds
- Cartridge headstamp: shotshells
- Cartridge headstamp: what it doesn’t tell you
- When to ask a gunsmith
- Common mistakes
- Tell us about your ammo
- FAQs
Cartridge Headstamp: The Short Answer
A cartridge headstamp is the marking pressed into the base of a cartridge case or shotshell. SAAMI defines it as the mark that identifies the maker and the caliber or gauge, sometimes with other information.
On a centerfire round it circles the primer. Read it with the cartridge standing on its nose and the base facing you.
SAAMI’s list of generally accepted cartridge and chamber names calls the headstamp the best way to verify you’re using the correct ammunition. It’s the simplest way to catch a wrong round before it goes into the gun.
Cartridge Headstamp: What the Markings Mean
Most commercial headstamps carry two things: who made the case and the cartridge name. A Small Arms Survey brief on ammunition marking notes that civilian case markings are usually limited to the manufacturer and the caliber.
Some cases carry more. Here’s what you may see.
| Marking | What it tells you | Example |
|---|---|---|
| Maker’s name, initials or logo | Who made the case | A brand name or its initials |
| Cartridge name | Which cartridge the case is | 9MM LUGER, 38 SPL, 30-06 SPRG |
| +P | Loaded above standard pressure | 38 SPL +P |
| Two-digit number | Year of manufacture, mainly on military cases | 21 for 2021 |
| NATO symbol | Passed NATO interchangeability testing | Military 5.56 and 7.62 rounds |
| Gauge | Shotshell bore size | 12 GA, 20 GA |
The layout of a cartridge headstamp varies by maker. The cartridge name is the part that matters for safety.
Cartridge Headstamp: SAAMI Abbreviations
SAAMI’s pistol and revolver standard says its full or abbreviated cartridge names should be used on headstamps and on firearm markings. That shared vocabulary is what lets you compare the two.
These abbreviations come from SAAMI’s names list and its interchangeability list.
| Cartridge (SAAMI full name) | SAAMI abbreviation | Also known as |
|---|---|---|
| 9mm Luger | 9MM LUGER | 9mm Parabellum, 9x19mm |
| 380 Automatic | 380 AUTO | 380 ACP, 9mm Kurz |
| 45 Automatic | 45 AUTO | 45 ACP |
| 38 Special | 38 SPL | 38 S&W Special, 38 Colt Special |
| 357 Magnum | 357 MAG | — |
| 44 Remington Magnum | 44 REM MAG | 44 Magnum |
| 30-06 Springfield | 30-06 SPRG | 30 GOV’T -06, 7.62x63mm |
| 22 Long Rifle | 22 LR | — |
A headstamp may show the full name, the abbreviation or an alternate name. “45 ACP” and “45 AUTO” are the same round; “38 SPL” and “357 MAG” are not.
Our guide to common ammo calibers explains how these names came about.
Cartridge Headstamp: How to Read One
Run through these steps every time you load from a new box or a bag of loose rounds.
- Find your firearm’s marking. SAAMI says it’s usually on the barrel, and sometimes on the frame or receiver.
- Read the cartridge headstamp. Turn the round base-up in good light; a magnifier helps on worn or small cases.
- Match the full cartridge name, not just the number. A 38 SPL round in a 357 Magnum is an approved pairing; a 357 MAG round in a 38 Special is not.
- Check the box too. It shows the bullet weight, bullet type and lot number.
- Stop if anything disagrees. SAAMI’s interchangeability list is blunt: if you have any doubt about the designation, don’t use the ammunition.
SAAMI also warns that a round fitting the chamber is not proof it’s safe to fire. Our beginner’s guide to buying ammo walks through the rest of the box label.
Cartridge Headstamp: Similar Names That Don’t Mix
Cartridges with similar names are where a cartridge headstamp earns its keep. SAAMI’s interchangeability list approves only a few alternate cartridges for each chamber.
- 38 SPL and 357 MAG. SAAMI lists 38 Special as safe in a 357 Magnum chamber, never the reverse. Our .357 Magnum vs .38 Special comparison explains why; shop 38 Special ammo or 357 Magnum ammo.
- 44 S&W SPL and 44 REM MAG. The same pattern: 44 Special in a 44 Magnum, never the reverse. Shop 44 Special ammo or 44 Magnum ammo.
- 22 Short, 22 Long and 22 LR. SAAMI approves all three in a 22 Long Rifle chamber. Shop .22 LR ammo.
- 223 REM and 5.56 NATO. SAAMI’s FAQ says .223 Remington can be fired in a military-spec 5.56 chamber, with the firearm maker’s confirmation. Firing 5.56 in a barrel marked .223 Remington can push pressure to dangerous levels; see our 5.56 vs .223 deep dive.
- 308 WIN and 7.62×51 NATO. SAAMI warns that some surplus military rifles have headspace acceptable for military ammunition but excessive for commercial cartridges, and uses this pair as its example. Shop 308 ammo or 7.62×51 NATO ammo only for firearms marked for each.
Cartridge Headstamp: +P Markings
SAAMI’s pistol and revolver standard says +P ammunition is loaded to higher pressure, shown by a +P marking on the case headstamp. It should be used only in firearms designed and recommended for it by the manufacturer.
Check your manual before you buy. If it doesn’t approve +P, choose standard-pressure loads.
You may also see +P+ on some boxes. SAAMI’s pistol standard doesn’t cover +P+, so no industry pressure figure stands behind it; follow your firearm’s manual.
Cartridge Headstamp: Military and NATO Marks
Military cases follow their own rules. The Small Arms Survey brief says that under NATO standardization agreements, a military cartridge headstamp should show a NATO design mark, a producer code and the last two digits of the production year.
The NATO mark has a specific meaning. A 2022 European Security & Defence article on ammunition interchangeability explains that producers may put NATO’s interchangeability symbol on the headstamp and packaging only after the ammunition passes testing at NATO’s two independent test centers, in the US and the UK.
Two cautions for shooters:
- Military ammunition belongs in firearms marked for it. SAAMI says to fire it only in firearms explicitly marked and chambered for that cartridge.
- Some military rounds have no headstamp at all. SAAMI says to check the original packaging instead, and not to fire a round you can’t identify.
Foreign and older surplus headstamps may use other alphabets or number-only factory codes, which the Small Arms Survey notes are easy to misread. Collectors at the International Ammunition Association, a nonprofit collectors’ group, discuss unusual headstamps on its forum.
Cartridge Headstamp: Rimfire Rounds
Don’t be surprised if your .22 LR has no cartridge headstamp. SAAMI notes that rimfire ammunition often lacks headstamp markings.
That makes the box your proof of identity. Keep rimfire in its original packaging rather than loose in a range bag; our guide to storing ammunition covers the rest.
The difference between the two ignition systems is explained in rimfire vs centerfire ammo.
Cartridge Headstamp: Shotshells
On a shotshell, the headstamp sits on the metal head and identifies the maker and the gauge. The gauge is the critical part.
SAAMI says different gauges are never interchangeable. A 20 gauge shell loaded into a 12 gauge can plug the bore, and SAAMI calls the result a “12/20 burst”; 16 in 12, 20 in 16 and 28 in 20 are risky for the same reason.
Shell length matters too. Shorter shells can generally be fired in a longer chamber of the same gauge, but SAAMI warns that a shell longer than the chamber can produce excessive pressure.
Confirm shell length from the box and the barrel marking, and store 12 and 20 gauge shells in separate, labeled containers. Our shotgun gauges guide and 12 gauge vs 20 gauge comparison go deeper; shop 12 gauge shells or 20 gauge shells.
Cartridge Headstamp: What It Doesn’t Tell You
A cartridge headstamp identifies the case, not the whole load. The box fills in the rest.
- Bullet weight and type. Grains, FMJ or JHP are printed on the box, not the case. Our ammo glossary defines each term.
- Lot number. The Small Arms Survey notes that lot numbers live on the packaging, so a round that leaves its box can no longer be linked to its production lot.
- Who loaded it. The headstamp is pressed in when the case is made, so on reloaded or remanufactured ammunition it shows the original case maker, not the company that loaded the round. Read is reloading worth it before buying or making reloads.
- Condition. A clean headstamp says nothing about corrosion or damage; our ammo myths guide shows the warning signs.
When to Ask a Gunsmith
Have a qualified gunsmith look before you fire if any of these apply.
- The headstamp is worn or unreadable and there’s no box
- The headstamp and the box disagree
- Surplus or foreign rounds you can’t identify. SAAMI says not to fire them until a qualified person has examined them.
- The marking on your firearm is worn or unclear
- You plan to shoot commercial ammunition in a military surplus rifle
- Anything feels unsafe
Common Mistakes
- Going by the number alone. 38 SPL and 357 MAG share a bullet diameter, not a chamber.
- Assuming a round that chambers is safe. SAAMI says fit is not proof.
- Mixing loose rounds from different boxes. The headstamp is then your only check.
- Firing +P in a firearm not approved for it.
- Carrying 12 and 20 gauge shells in the same pouch.
- Treating the headstamp brand as the loader on remanufactured ammunition.
- Throwing away rimfire and surplus boxes, which carry the identity and lot number.
How We Can Help
Not sure what you have? Note the exact marking on your firearm and the full cartridge headstamp, then reach us through our contact page.
We can help you find matching ammunition. We can’t inspect rounds remotely, so unidentified ammunition still needs a gunsmith.
Browse by type: handgun ammo, rifle ammo, rimfire ammo and shotgun ammo.
Tell Us About Your Ammo
Shooters spot markings no catalog explains. Answer any of these in the comments to help other readers of this cartridge headstamp guide.
- What’s the oddest headstamp you’ve found?
- Where is the cartridge marking on your firearm?
- Have two similar cartridge names ever caught you out?
- Which headstamp abbreviation confused you at first?
Share what you can and we’ll join in with general guidance. Please don’t post personal contact details or payment information.
Before You Go
Ready to buy the right round? Match the headstamp to your firearm’s marking, then shop by cartridge name.
- Shop handgun ammo by cartridge and pressure rating
- Shop rifle ammo by cartridge, commercial or NATO
- Shop shotgun ammo by gauge and shell length
- Shop all ammunition now →
Need a term from the box explained? Our ammo glossary covers 104 of them.
This cartridge headstamp guide is general educational information, not professional safety advice. Always follow your firearm manufacturer’s instructions and the markings on your firearm. If you’re unsure what a round is, don’t fire it; have a qualified gunsmith examine it. Laws on buying, transporting and using ammunition vary by state and locality.
Cartridge Headstamp FAQs
What is a cartridge headstamp?
The marking pressed into the base of a case or shotshell. It identifies the maker and the caliber or gauge, sometimes with more information.
Where do I find the headstamp?
On the flat base of the case. On centerfire ammunition it circles the primer.
What does +P on a headstamp mean?
The round is loaded above standard pressure for that cartridge. Use it only if your firearm’s manufacturer approves +P.
Does the cartridge headstamp show bullet weight?
No. Bullet weight and type are on the box.
Why doesn’t my .22 LR have a headstamp?
Rimfire ammunition often has none, SAAMI notes. Keep it in the original box so you can identify it.
What does the NATO mark on a headstamp mean?
The ammunition passed NATO interchangeability testing. Fire military ammunition only in firearms marked for that cartridge.
Does a headstamp show when ammo was made?
Military headstamps usually show the last two digits of the year. Commercial headstamps usually don’t.
Is the headstamp the same as the lot number?
No. The lot number is on the box, so keep the box with the ammunition.
Can I fire a round if the headstamp doesn’t match my firearm?
No. SAAMI says not to use ammunition if you have any doubt about its designation, unless it’s on SAAMI’s short list of approved alternates.
The headstamp shows a different brand from the box. Is that a problem?
Not always: on reloaded or remanufactured ammunition, the headstamp shows the original case maker. If the cartridge name doesn’t match the box, don’t fire it and contact the company that sold it.
