Ammo Glossary: 100+ Essential Ammunition Terms Explained

Ammo boxes are full of shorthand: FMJ, +P, 124 gr, 2¾”, 00 buck. This ammo glossary translates 104 of those ammunition terms into plain English.

Terms are grouped by topic, so related words sit together. Where an industry definition exists, this ammo glossary follows SAAMI, the Sporting Arms and Ammunition Manufacturers’ Institute, which sets the voluntary standards U.S. ammunition makers follow.

Last reviewed: October 12, 2026.

The one rule that matters most: fire only the cartridge marked on your firearm’s barrel or slide. Check it against the headstamp on the case or the label on the box before you load.

In This Guide

• Ammo glossary: cartridge basics
• Ammo glossary: names and compatibility
• Ammo glossary: case and primer terms
• Ammo glossary: bullet types
• Ammo glossary: weight, speed and pressure
• Ammo glossary: shotgun and shotshell terms
• Ammo glossary: reading the box
• Ammo glossary: malfunctions and safety
• Ammo glossary: buying, storage and legal terms
• Common terminology mistakes
• When to stop and ask a gunsmith
• Tell us about your ammo
• FAQs

Ammo Glossary: Cartridge Basics

Every modern round has four parts: a case, a primer, propellant and a projectile. This part of the ammo glossary covers them first.

Ammunition (ammo). Loaded cartridges or shotshells ready to fire. One complete cartridge is a “round,” so a box of 50 rounds holds 50 cartridges.

Cartridge. A complete unit of ammunition: a case, primer and powder, usually with a bullet. SAAMI’s definition also counts shotshells as cartridges.

Bullet. The single projectile fired from a rifle or handgun, and only the part that leaves the barrel. Our guide to bullet types and when to use each covers the designs.

Projectile. Anything a firearm launches downrange: a bullet, a slug or a charge of shot pellets.

Case (casing, brass). The container that holds the other parts together, usually brass, steel or aluminum. Shotshells use a plastic hull with a metal head.

Primer. The impact-sensitive cap in the base of a centerfire case. When the firing pin strikes it, it sends a flame into the powder.

Propellant (powder). The fuel inside the case. Modern ammunition uses smokeless powder, which burns very fast to make high-pressure gas; black powder is the older propellant used in muzzleloaders.

Headstamp. Letters and numbers pressed into the base of a case or shotshell. According to SAAMI, it identifies the maker and the caliber or gauge.

Matching the headstamp to your firearm’s marking is the fastest compatibility check.

Shotshell. The shotgun version of a cartridge: a hull holding a primer, powder, a wad and either shot or a slug.

Ammo Glossary: Names and Compatibility

Cartridge names are labels, not measurements. This is the part of the ammo glossary that matters most for safety.

SAAMI. The Sporting Arms and Ammunition Manufacturers’ Institute, founded in 1926 at the federal government’s request. It sets voluntary standards for cartridge and chamber dimensions, pressure and interchangeability.

Caliber. A loose word with three uses: the approximate bore diameter (.30 caliber is about 0.30 inch), the cartridge a firearm fires (“a .308 rifle”), or a number in a cartridge name. SAAMI recognizes all three, so caliber alone never proves two rounds are interchangeable.

Our guide to common ammo calibers compares the popular ones.

Caliber vs. cartridge. Caliber describes a size; a cartridge is one specific round. The .38 Special and .357 Magnum both use bullets about 0.357 inch across, yet they are different cartridges with different lengths and pressures.

Cartridge name (designation). The name on the box, such as 9mm Luger or 6.5 Creedmoor. Names mix inches, millimeters, companies and dates: .30-06 means .30 caliber, adopted in 1906.

Metric designation. Bullet diameter × case length in millimeters, such as 9x19mm or 7.62x39mm. The second number separates cartridges that share a bullet diameter.

Equivalent names. Some cartridges sell under several names. 9mm Luger, 9mm Parabellum and 9x19mm are one round, as are .45 Auto and .45 ACP; SAAMI keeps a list of generally accepted cartridge and chamber names.

Chamber. The part of the barrel, or a revolver’s cylinder, that holds the cartridge as it fires.

Chambered for. The cartridge a firearm is built to fire, stamped on the barrel or slide. This marking, not the caliber number, decides what you can load.

Interchangeability. Whether one cartridge can safely fire in a chamber made for another. SAAMI’s interchangeability list allows only a few pairs, such as .38 Special in a .357 Magnum and .22 Short or .22 Long in a .22 LR chamber.

Never assume the reverse works. See our .357 Magnum vs .38 Special comparison.

5.56 NATO vs. .223 Remington. Nearly identical outside, different chambers. SAAMI’s FAQ says .223 Remington ammunition can be fired in a military-spec 5.56 chamber with the firearm maker’s confirmation, but 5.56 ammunition in a barrel marked .223 Remington can reach dangerous pressure.

Our 5.56 vs .223 deep dive explains why.

Magnum. A naming convention for a more powerful version of a cartridge, usually with a longer or larger case, as in .357 Magnum. On shotshells it means a longer or heavier load.

NATO (military-spec). Ammunition made to NATO standards, such as 5.56x45mm and 7.62x51mm NATO. Treat it as a different cartridge from the commercial version unless your firearm’s maker says otherwise.

Wildcat. A non-standard cartridge made by reshaping an existing case. With no SAAMI specification, its dimensions can vary by maker.

Ammo Glossary: Case and Primer Terms

This section of the ammo glossary explains how a case’s shape and priming decide which firearm it fits and whether it can be reloaded.

Rimfire. Priming compound spun into the hollow rim; the firing pin crushes the rim to fire it. The .22 LR, .22 WMR and .17 HMR are rimfire, and the cases can’t be reloaded.

More in rimfire vs centerfire ammo.

Centerfire. A cartridge with a separate primer in the center of the case head. Nearly all handgun, rifle and shotgun ammunition is centerfire.

Boxer primer. The primer used in most U.S. commercial ammunition. Its anvil is built in and the case has one central flash hole, so the case can be reloaded.

Berdan primer. A primer whose anvil is part of the case, with two or more small flash holes. It’s common in steel-cased and some imported ammunition, and hard to reload.

Corrosive primer. A primer with salts that cause rust if the bore isn’t cleaned after shooting. It turns up in some older military surplus; modern commercial ammunition is non-corrosive.

Rimmed. A rim wider than the case body, as on the .38 Special and .30-30 Winchester.

Rimless. A rim the same diameter as the body, with an extractor groove ahead of it, as on the 9mm Luger and .308 Winchester.

Belted. A raised band ahead of the extractor groove, used on many magnum rifle cases such as the 7mm Remington Magnum.

Straight-wall. A case with nearly parallel sides and no shoulder, such as the 9mm and .350 Legend. Several states allow straight-wall rifle cartridges for deer where bottleneck rounds are restricted.

See our straight-wall cartridge states guide, and confirm current rules with your state wildlife agency.

Bottleneck. A case that narrows at a shoulder into a neck that grips a smaller bullet, as on the .223 Remington and 6.5 Creedmoor.

Headspace. The distance from the closed bolt face to the point in the chamber that stops the cartridge moving forward, as defined by SAAMI. Headspace problems are a job for a gunsmith.

Crimp. The case mouth squeezed onto the bullet, or folded shut on a shotshell, to hold everything in place.

Brass case. The traditional case material. Brass seals the chamber, extracts smoothly and can be reloaded.

Steel case. A coated steel case, usually cheaper than brass and generally not reloadable. Many indoor ranges restrict it; compare the two in brass vs steel ammo.

Aluminum case. A lightweight, low-cost case used in some range ammunition. It isn’t reloadable.

Nickel-plated case. Brass with a nickel finish that resists corrosion, common on defensive handgun ammunition.

Ammo Glossary: Bullet Types

Bullet construction decides what happens on impact. Each abbreviation in this part of the ammo glossary matches one you’ll see on a box.

FMJ (full metal jacket). A lead core inside a copper-alloy jacket that doesn’t expand; the military calls it “ball.” It’s the standard practice round, as our hollow point vs FMJ comparison explains.

TMJ (total metal jacket). FMJ with the base covered too, which reduces airborne lead at indoor ranges.

JHP (jacketed hollow point). A jacketed bullet with a nose cavity designed to expand. How much it expands depends on velocity and what it hits.

Soft point (SP, JSP). A jacketed bullet with exposed lead at the tip for controlled expansion, a classic hunting design.

Polymer tip (ballistic tip). A plastic-tipped bullet that streamlines the nose and helps start expansion.

Bonded. A bullet with its jacket fused to the core so the two stay together on impact.

Monolithic (solid copper). A single-metal bullet with no lead core, common where lead-free hunting ammunition is required.

OTM (open tip match). A match bullet with a small tip opening left by manufacturing. It isn’t designed to expand like a hollow point.

Boat tail. A tapered bullet base that reduces drag at long range.

Spitzer. A pointed nose, from the German word for “pointed,” found on most rifle bullets.

Round nose (RN, LRN). A rounded profile. LRN means unjacketed lead round nose, common in revolver loads.

Wadcutter (WC). A flat-fronted cylinder that cuts clean holes in paper targets.

Semi-wadcutter (SWC). A wadcutter with a short cone nose that feeds more smoothly.

Frangible. Compressed metal powder that breaks apart on hard surfaces. Some ranges require it for close-range steel targets.

Lead-free. Any load with no lead in the projectile. Some states, including California, require lead-free ammunition for hunting.

Ammo Glossary: Weight, Speed and Pressure

The numbers on a box are measured under test conditions that may not match your firearm. This ammo glossary section explains what each one means.

Grain (gr). The unit for bullet weight; one grain is 1/7,000 of a pound, about 64.8 milligrams. A “124 gr” 9mm load has a 124-grain bullet, not 124 grains of powder.

Our bullet grain weight guide explains how weight changes recoil and performance.

Muzzle velocity. The bullet’s speed as it leaves the barrel, in feet per second (fps).

Test barrel length. The barrel used to measure the velocity printed on the box. Your firearm may be faster or slower, so use box figures to compare loads.

Muzzle energy. The bullet’s energy at the muzzle in foot-pounds: bullet weight in grains × velocity² ÷ 450,240. It helps compare loads but doesn’t predict performance on its own.

Ballistic coefficient (BC). How well a bullet resists air drag; a higher BC holds speed better and drifts less. Compare only BCs that use the same drag model, G1 or G7.

Trajectory. The curved path a bullet follows as gravity pulls it down, shown as drop in ballistics tables.

Subsonic. Slower than sound, about 1,125 fps at sea level on a mild day. Subsonic loads are quieter because they make no sonic crack.

Supersonic. Faster than sound. Most rifle ammunition is supersonic.

Chamber pressure. The peak gas pressure when a round fires, usually in pounds per square inch (psi). SAAMI notes that older units, such as CUP, can’t be converted to psi with a formula.

MAP (maximum average pressure). SAAMI’s term for the highest average pressure its standards allow for a cartridge.

+P. Loaded above the standard SAAMI pressure for that cartridge, such as 9mm +P or .38 Special +P. Use it only in firearms whose manufacturer approves +P.

+P+. Loads above +P. There is no SAAMI standard for +P+, and many firearm manufacturers prohibit it.

Cartridge overall length (COL). The length of a loaded round from base to bullet tip. SAAMI drawings set the maximum so rounds fit magazines and chambers.

Bullet setback. A bullet pushed deeper into its case, often by chambering the same round again and again. It can raise pressure, so don’t fire a round that sits visibly deeper than the rest.

Ammo Glossary: Shotgun and Shotshell Terms

Gauge sizes the bore, shell length must match the chamber, and shot sizes run backwards. These ammo glossary entries cover the words printed on shotshell boxes.

Gauge. The number of bore-diameter lead balls that together weigh one pound, so a lower number means a bigger bore. Our shotgun gauges guide compares 12, 20, 28 gauge and .410.

.410 bore. Named for its bore diameter in inches, not by gauge. Expressed as a gauge, it would be about 67.

Shell length. A shell’s length after firing, once the crimp opens, such as 2¾”, 3″ or 3½” in 12 gauge.

Chamber length. The longest shell a shotgun is built to fire, marked on the barrel. Never fire a shell longer than the chamber.

Hull. The plastic body of a shotshell, with its metal head.

Wad. The plastic or fiber piece that separates the powder from the shot and cushions the payload.

Shot size. Pellet diameter. For birdshot, a bigger number means a smaller pellet (#9 is smaller than #4); buckshot has its own scale, where 00 is larger than #4 buck.

Birdshot. Small shot for birds, small game and clay targets. See buckshot vs birdshot.

Buckshot. Large shot for deer where legal and for defense. A typical 12 gauge 00 buck load holds eight or nine pellets of about .33 inch each.

Slug. A single heavy shotgun projectile. Foster slugs suit smooth barrels; sabot slugs are designed for rifled barrels.

Payload. The weight of shot in a shell, given in ounces, such as 1⅛ oz.

Dram equivalent. An old marking that compares a smokeless load’s velocity with a black-powder load. SAAMI notes modern shells run at roughly the same pressure whatever the figure.

Choke. A constriction at the muzzle that controls how tightly shot spreads, from cylinder to full. Our choke and shot size guide matches chokes to loads.

Pattern. The spread of pellets on paper at a set distance, which shows how a load and choke perform together.

Non-toxic shot. Steel, bismuth or tungsten-alloy shot. Federal rules have required approved non-toxic shot for hunting ducks, geese, swans and coots nationwide since 1991, according to the U.S. Fish & Wildlife Service.

Not every lead-free pellet qualifies: a 2026 Service memo confirms pure copper shot isn’t approved. See our non-toxic waterfowl ammo guide.

TSS (tungsten super shot). Very dense tungsten-alloy shot that lets hunters use smaller pellets at longer range, at a much higher price per shell.

Ammo Glossary: Reading the Box

Most of what you need to identify ammunition is printed on the box or stamped on the case. This part of the ammo glossary helps you decode it.

Lot number. A production code on the box or carton that identifies the batch. Keep it in case you need to contact the manufacturer or check a recall.

Rounds per box. Twenty is common for rifle loads, 25 for shotshells and 50 for many handgun loads. A bulk “case” is a carton of many boxes, not a cartridge case.

Ballistics data. Velocity, energy and drop figures on the box or the maker’s site, measured from a test barrel.

Factory new. Ammunition loaded by the manufacturer with all-new components.

Remanufactured (reman). Commercially loaded ammunition built on previously fired, reprocessed cases. It’s usually cheaper than factory new.

Reloads (handloads). Ammunition assembled by an individual rather than a factory. Many firearm warranties exclude damage from reloads, and you should never fire handloads of unknown origin.

Thinking of loading your own? Read is reloading worth it first.

Military surplus. Ammunition sold from military stocks. It can be decades old, and some older surplus uses corrosive primers.

Match grade. Ammunition built for consistency and accuracy with premium bullets, priced above range ammo.

Range ammo. Lower-cost practice ammunition, usually FMJ, for training and plinking.

Defensive (duty) ammo. Premium expanding ammunition, usually JHP, designed for self-defense. See our home defense ammo guide.

Ammo Glossary: Malfunctions and Safety

When a round doesn’t fire normally, stop and keep the muzzle pointed in a safe direction. The ammo glossary terms below describe what may have happened; your firearm’s manual says what to do next.

Misfire. A round that doesn’t fire after a proper primer strike, as SAAMI defines it. Keep the muzzle safe and wait before opening the action; SAAMI advises several seconds, and your manual or range may require longer.

Hangfire (delayed fire). A noticeable delay between the primer strike and the shot, which SAAMI calls a delayed fire. It’s the reason to wait after any failure to fire.

Squib load. An abnormally weak round that fires with a pop and can leave the bullet stuck in the barrel, per SAAMI. Stop and have the barrel checked, because firing into a blocked barrel can destroy the firearm and injure you.

Case head separation. A case tearing apart near its base during firing. Worn or corroded cases and headspace problems can cause it.

Tarnish vs. corrosion. Dull, dark brass is cosmetic; green, white or crusty growth means the metal is being eaten away. Don’t fire corroded rounds. Our ammo myths guide shows the difference.

Ammo Glossary: Buying, Storage and Legal Terms

These ammo terms come up most when you compare prices, store ammunition and check whether an order can ship to you.

Cost per round (CPR). The box price divided by the number of rounds. An $18 box of 50 works out to $0.36 per round.

Bulk ammo. Large quantities, such as 500 or 1,000 rounds, usually cheaper per round. Our bulk ammo buying guide shows when it pays off.

Shelf life. How long ammunition stays reliable; storage conditions matter more than age. SAAMI publishes storage and handling recommendations, and our guide to storing ammunition turns them into a checklist.

FFL (Federal Firearms License). A license held by firearm dealers, manufacturers and importers; firearms bought online ship to an FFL holder. Federal law doesn’t require an FFL for most ammunition purchases, but some states and cities add their own rules.

NFA (National Firearms Act). The 1934 federal law that regulates suppressors, short-barreled rifles and shotguns, machine guns and certain other items. Standard ammunition isn’t covered by it.

Shipping restrictions. State, local and carrier rules that limit where ammunition can ship. Our guide to buying ammo online legally explains how federal and state rules fit together.

Common Terminology Mistakes

These are the mix-ups this ammo glossary is built to prevent.

• Reading “gr” as powder weight. On the box, it’s the bullet’s weight.
• Treating caliber as the cartridge. The .38 Special and .357 Magnum share a bullet diameter, not a chamber.
• Assuming 5.56 and .223 are the same. Go by the marking on the barrel.
• Buying shotshells by gauge alone. Shell length must fit the chamber too.
• Firing +P in a firearm not rated for it.
• Re-chambering the same defensive round every day. It invites bullet setback.
• Ignoring a weak “pop” and firing again. Stop and check for a squib.

When to Stop and Ask a Gunsmith

No ammo glossary replaces a gunsmith. Ask a qualified one before shooting again if you see any of these.

• A squib, or anything stuck in the bore
• Split cases or a case head separation
• Repeated misfires or hangfires with ammunition that should be good
• Flattened or pierced primers, or cases that stick in the chamber
• Ammunition you can’t identify from the headstamp or box
• Anything that feels unsafe

How We Can Help

Not sure which box matches your firearm? Note the exact marking on your barrel or slide and the cartridge name on the box, then reach us through our contact page. The same goes for any word you need that isn’t in this ammo glossary yet.

Browse by type: handgun ammo, rifle ammo, rimfire ammo and shotgun ammo. Popular starting points are 9mm ammo, .223 Remington ammo, .22 LR ammo and 12 gauge shells.

Tell Us About Your Ammo

Shooters learn words no catalog explains. Answer any of these in the comments to help other readers of this ammo glossary.

• Which term confused you most when you started buying ammo?
• Which word is missing from this list?
• What’s printed on a box you’ve never understood?
• Have two similar cartridge names ever caught you out?

Share what you can and we’ll join in with general guidance; missing words go into the next ammo glossary update. Please don’t post personal contact details or payment information.

Before You Go

Ready to put the terms to work? Match the headstamp to your barrel marking, then shop by type.

• Shop handgun ammo by cartridge and bullet type
• Shop rifle ammo by cartridge and grain weight
• Shop shotgun ammo by gauge and shell length
• Shop all ammunition now →

Bookmark this ammo glossary for the next time a box uses a word you don’t know.

This ammo glossary is general educational information, not legal or professional safety advice. Always follow your firearm manufacturer’s instructions and the markings on your firearm and ammunition. Laws on buying, shipping, transporting and using ammunition vary by state and locality, so confirm current requirements with official sources.

Ammo Glossary FAQs

What’s the difference between a bullet and a cartridge?

The cartridge is the whole round: case, primer, powder and bullet. The bullet is only the projectile that leaves the barrel.

What does “gr” mean on an ammo box?

Grains, the unit for bullet weight. A 124 gr bullet weighs about 8 grams.

What does +P mean?

Higher pressure than the standard load for that cartridge. Use it only if your firearm’s manufacturer approves +P.

Can I shoot .223 in a 5.56 rifle?

SAAMI says .223 Remington can be fired in a military-spec 5.56 chamber, with the firearm maker’s confirmation. The reverse isn’t recommended.

What does a headstamp tell me?

The maker and the cartridge or gauge. Compare it with your firearm’s marking before loading.

Why does a smaller gauge number mean a bigger shotgun?

Gauge counts how many bore-sized lead balls weigh one pound. Fewer, bigger balls fit a 12 gauge, so it’s larger than a 20.

What should I do if a round doesn’t fire?

Keep the muzzle pointed safely and wait before opening the action, in case it’s a delayed fire. Follow your manual or range rules on how long.

What is a lot number used for?

It identifies the production batch, which manufacturers use to trace quality problems and recalls.

How was this ammo glossary checked?

Industry terms were compared with SAAMI’s glossary and technical documents, and hunting terms with U.S. Fish & Wildlife Service guidance. This ammo glossary was last reviewed in October 2026.

Where should a beginner start in this ammo glossary?

Start with cartridge basics and names and compatibility. Those two sections cover the terms that matter most for safety.