Bullet Sizes and Caliber Chart (Rifle and Handgun)

Caliber is not as simple as “the exact size of the bullet.” SAAMI defines caliber as a firearm chambering term, an approximate barrel land diameter term, and a number in a cartridge name that only roughly approximates bullet diameter. That is why 38 Special, 357 Magnum, and 9 mm Luger can be confusing at first glance. Always match ammunition to the firearm’s marking and the ammunition headstamp or package, because similar size does not mean interchangeable.

Caliber, cartridge, and bullet: the basic terms

SAAMI defines a cartridge as one complete round of ammunition made from a case, primer, propellant, and one or more projectiles. In everyday speech, people often say “bullet” when they mean the whole cartridge, but the bullet is only the projectile portion.

Caliber can mean several related things. SAAMI’s glossary gives three beginner-useful meanings: the cartridge a firearm is chambered for, the approximate diameter formed by the tops of the lands in a rifled barrel, and the numerical part of a cartridge name that roughly approximates bullet diameter.

That last part is the key. A cartridge name is a label. It may be based on inches, millimeters, a case length, an older naming convention, a maker name, or a marketing name. It is not a guarantee that the number in the name is the exact projectile diameter.

The safety rule: match the firearm marking

SAAMI’s 2021 interchangeability advisory says firearms should only be used with ammunition designated by the firearm manufacturer for that firearm. SAAMI also warns that just because a round can fit into a firearm’s chamber, barrel, or action, that does not necessarily make it safe to use.

SAAMI says the best way to verify correct ammunition is to check the ammunition headstamp against the firearm marking. This matters because cartridges can share similar names or similar projectile dimensions while still being different cartridges.

One clear example from SAAMI is 223 Remington and 5.56 NATO. SAAMI states that 5.56, 5.56 NATO, or 5.56x45 mm ammunition is not safe to shoot in a barrel marked 223 Remington.

Why caliber names do not always match bullet diameter

Some caliber names are close to the projectile diameter. Others are legacy names that make more sense after you see the cartridge drawing.

Cartridges with similar projectile dimensions should not be treated as interchangeable based on projectile diameter alone. Interchangeability is controlled by the firearm’s chambering and the manufacturer’s ammunition designation.

SAAMI also has naming conventions that may look different from casual writing. SAAMI says a decimal point is never included before the numerical caliber component of any cartridge name. For example, SAAMI recognizes names such as 380 Automatic (380 Auto) and 45 Automatic (45 Auto), rather than writing them with a leading decimal point.

Bullet size and caliber chart

The chart below is a beginner reference for common cartridge names. Example bullet weights can vary by load and maker.

Cartridge	Handgun or rifle	Example factory bullet weights	Beginner note
22 Long Rifle	Handgun entry	Check the ammunition package or current manufacturer catalog	C.I.P. lists the cartridge as 22 Long Rifle.
380 Auto	Handgun	Check the ammunition package or current manufacturer catalog	C.I.P. lists 9 mm Browning court with alternate names including 380 ACP and 380 Auto. SAAMI recognizes 380 Automatic (380 Auto).
9 mm Luger	Handgun	Check the ammunition package or current manufacturer catalog	A 9 mm style label is still a cartridge name, not a general interchangeability rule.
38 Special	Handgun	Check the ammunition package or current manufacturer catalog	The name “38” is not the projectile diameter.
357 Magnum	Handgun	Check the ammunition package or current manufacturer catalog	Do not use projectile diameter alone to decide interchangeability.
40 S&W	Handgun	Check the ammunition package or current manufacturer catalog	C.I.P. lists a 10.17 mm projectile G1 dimension.
10 mm Auto	Handgun	Check the ammunition package or current manufacturer catalog	C.I.P. lists the same projectile G1 dimension as 40 S&W, but they are different cartridges.
44 Remington Magnum	Handgun	Check the ammunition package or current manufacturer catalog	Always match the exact cartridge designation on the firearm and ammunition.
45 Auto	Handgun	Check the ammunition package or current manufacturer catalog	SAAMI recognizes 45 Automatic (45 Auto).
223 Rem	Rifle	Check the ammunition package or current manufacturer catalog	SAAMI states that 5.56 NATO or 5.56x45 mm ammunition is not safe in a barrel marked 223 Remington.
6.5 Creedmoor	Rifle	Check the ammunition package or current manufacturer catalog	The name uses a 6.5 mm style label.
270 Win	Rifle	Check the ammunition package or current manufacturer catalog	C.I.P. lists 270 Win with a 7.06 mm projectile G1 dimension.
308 Win	Rifle	Check the ammunition package or current manufacturer catalog	Always match the exact cartridge designation on the firearm and ammunition.
30-06 Springfield	Rifle	Check the ammunition package or current manufacturer catalog	Always match the exact cartridge designation on the firearm and ammunition.

Reading the chart without getting tripped up

Start with the cartridge name, not the bullet diameter. The firearm is chambered for a cartridge, and SAAMI describes caliber first as a term used to designate the specific cartridge or cartridges for which a firearm is chambered.

Next, look at the cartridge designation as the starting point. It helps explain why some names look odd. Similar looking names or numbers can still refer to separate cartridges with different names and specifications.

Then look at bullet weight separately. A bullet weight, usually given in grains, describes one load option within that cartridge.

Bullet weight does not identify the cartridge by itself. Different cartridges can use bullets of similar weight, and one cartridge can be loaded with more than one bullet weight.

Common naming quirks beginners notice

9 mm Luger, 9 mm Parabellum, and 9 x 19 mm

Beginners may see more than one name in discussions of this cartridge, so the safest habit is to follow the exact designation on the firearm and ammunition.

38 Special and 357 Magnum

Their names can mislead beginners because the number in a cartridge name is not always a direct projectile measurement. Use the firearm chambering and ammunition designation, not name similarity, to decide what belongs in a firearm.

40 S&W and 10 mm Auto

C.I.P. lists both 40 S&W and 10 mm Auto with a projectile G1 dimension of 10.17 mm. They are separate cartridge names and should not be treated as interchangeable based on projectile dimension.

308 Win and 30-06 Springfield

These rifle cartridge names are separate designations. Do not infer interchangeability from similar numbers or similar bullet size.

What to check before buying or using ammunition

Check the exact cartridge marking on the firearm. Then check the ammunition headstamp and the ammunition package. SAAMI says the ammunition should match the firearm marking, and it warns that a cartridge fitting into the chamber, barrel, or action does not necessarily make it safe.

Also check the current ammunition maker’s catalog or package for the exact bullet weight and load information. Bullet weight information can change by load and maker.

When a name has more than one version, confirm the exact designation with the firearm maker and the ammunition maker. For standards details, SAAMI publishes safety, reliability, and interchangeability standards for commercial firearms, ammunition, and components, and C.I.P. publishes TDCC tables used for small-arms proof technical standards.