Light bullets
Many varmint-oriented loads use light bullets designed for rapid expansion. Their high muzzle velocity should not be confused with the behavior of a heavier match or hunting bullet.
THE CARTRIDGE LIBRARY · COMPACT RIFLE CARTRIDGE
5.56 NATO
A NATO rifle-cartridge designation closely related in external dimensions to .223 Remington. Military load names identify specific projectiles and specifications within that family.
2A Ledger reference desk · Sources checked October 18, 2026
Bullet diameter · reference0.2244 in5.700 mm
Know the exact name
At a glance
- Cartridge family
- Compact rifle cartridge
- Bullet specification
- 0.2244 in / 5.700 mmReference bullet Ø
- Factory examples
- 6 loadsSelected, sourced examples below
- Weight in cited examples
- 55–75 grGrains measure mass, not powder charge
5.56 NATO is identified by its complete cartridge designation. The resource-table alternative is 5.56 × 45 mm NATO. A caliber number, bullet diameter, or family resemblance on its own does not identify ammunition compatibility.
Do not treat 5.56 NATO and .223 Remington as a universal compatibility statement. Check the firearm manufacturer's chamber guidance.
Keep separate from .223 Remington. Identification reference; no NATO maximum is claimed.
Dimensions: open the named cartridge reference ↗. The displayed number is reference bullet ø, rather than an assertion that every manufactured projectile or barrel has this exact diameter.
Origins & evolution
Background & development
The 5.56 mm service-cartridge story began with the American search for a lighter rifle-and-ammunition system that led to the AR-15 and M16. Early U.S. ammunition used the M193 designation. The small, high-velocity cartridge reduced the weight of ammunition a soldier carried compared with the preceding full-power 7.62 mm rifle system, while changing the balance of recoil, range and projectile design.
The later NATO-era development was not just a new name for that original loading. Belgium’s SS109 projectile family led to the U.S. M855 ball cartridge, adopted by the Army in 1982, and was associated with the M249 and M16A2. The Army subsequently developed M855A1, fielded in 2010, as another distinct service loading. This history explains why 5.56 NATO encompasses several generations of ammunition. A cartridge-family label, a military load designation and a particular rifle’s chamber specification describe different parts of that evolving system.
Historical sources: U.S. Army: Evolution of the M855A1 Enhanced Performance Round ↗ · U.S. Army Infantry, September–October 1988: M249 and ammunition development ↗
Construction changes the story
Loads, variations & specialty offerings
Longer bullets
Streamlined match bullets can retain velocity differently downrange. Bullet length, construction, rifling twist, and magazine constraints are product-specific; grain weight alone does not describe them.
Specialty construction
Monolithic, bonded, tipped, and subsonic products are distinct load types when offered. A match label describes a target role and does not automatically establish a hunting application.
In the cited 5.56 NATO examples, bullet weights are 55, 62, 75 grains. These are the weights actually present in this source selection, not a claim that every possible loading is listed.
Bullet construction background: Hornady: anatomy of a bullet ↗. Exact product descriptions and velocities are cited in the factory table.
From the factory catalog
55 grains
3,165 fps
FMJ BT
62 grains
3,020 fps
FMJ BT
75 grains
2,910 fps
BTHP (20" Bbl)
Compare all 6 cited factory load records
| Maker / product | Bullet mass | Published construction | Muzzle velocity | Test barrel | Source |
|---|---|---|---|---|---|
| FederalAE193 | 55 gr 3.56 g | FMJ BT | 3,165 fps 965 m/s | 20 in | Federal · PDF pp. 58–59 ↗ |
| FederalAE193C | 55 gr 3.56 g | FMJ BT | 3,165 fps 965 m/s | 20 in | Federal · PDF pp. 58–59 ↗ |
| Hornady812544 | 55 gr 3.56 g | CX® (20" Bbl) | 3,175 fps 968 m/s | 20 in | Hornady · PDF p. 183 ↗ |
| FederalAE855 | 62 gr 4.02 g | FMJ BT | 3,020 fps 920 m/s | 20 in | Federal · PDF pp. 58–59 ↗ |
| Hornady81263 | 62 gr 4.02 g | FMJ (20" Bbl) | 3,060 fps 933 m/s | 20 in | Hornady · PDF p. 183 ↗ |
| Hornady81264 | 75 gr 4.86 g | BTHP (20" Bbl) | 2,910 fps 887 m/s | 20 in | Hornady · PDF p. 183 ↗ |
Explore the published data
Ballistics you can inspect
Select a legend entry to add or remove its line. Hover or tap a plotted point, or use the position slider. With the graph focused, arrow keys move the inspector. Solid dots identify source points; dashed connectors show estimates between them. Load construction, pressure category, and test setup can differ even at the same grain weight.
Read the original values as accessible tables
5.56 NATO: factory velocity downrange
| Exact load | Source | Published points |
|---|---|---|
| 55 gr Federal FMJ BT | Federal | 0: 3165; 100: 2772; 200: 2412; 300: 2080; 400: 1776; 500: 1506 |
| 62 gr Federal FMJ BT | Federal | 0: 3020; 100: 2749; 200: 2493; 300: 2252; 400: 2024; 500: 1810 |
| 75 gr Hornady BTHP (20" Bbl) | Hornady | 0: 2910; 100: 2676; 200: 2453; 300: 2242; 400: 2041; 500: 1851 |
| 55 gr Federal FMJ BT | Federal | 0: 3165; 100: 2772; 200: 2412; 300: 2080; 400: 1776; 500: 1506 |
| 55 gr Hornady CX® (20" Bbl) | Hornady | 0: 3175; 100: 2781; 200: 2420; 300: 2086; 400: 1781; 500: 1511 |
| 62 gr Hornady FMJ (20" Bbl) | Hornady | 0: 3060; 100: 2714; 200: 2394; 300: 2095; 400: 1820; 500: 1571 |
How to interpret the comparison
Changing bullet weight also often changes bullet design and propellant choice. Two curves are comparisons of the listed products, not a controlled experiment proving that bullet weight alone caused the difference. Catalog downrange points are projections under the maker’s conditions; barrel-study points are recorded observations in the study firearm.
Direct answers
Common questions
What is 5.56 NATO?
A NATO rifle-cartridge designation closely related in external dimensions to .223 Remington. Military load names identify specific projectiles and specifications within that family.
What diameter does 5.56 NATO use?
The named identification reference gives 0.2244 inches (5.700 mm), reference bullet ø. This reference value is different from a casual caliber nickname.
Are similarly named cartridges interchangeable?
Do not treat 5.56 NATO and .223 Remington as a universal compatibility statement. Check the firearm manufacturer's chamber guidance.
Are the graph values measured or estimated?
The downrange view uses the exact manufacturer catalog records shown in the source table. Dashed connectors and intermediate inspector values use linear interpolation between the displayed source points. Calculated energy uses the listed bullet mass and velocity.
Does higher energy mean the best load?
Energy is calculated from mass and velocity. It does not establish accuracy, expansion, penetration, pattern density, recoil, or suitability for a particular firearm. Use the exact product documentation and firearm manual.
Trace the facts
Sources & methodology
Compiled by 2A Ledger from the linked standards, manufacturer publications, and identified test records. Checked October 18, 2026. Historical tests and older catalogs retain their original dates; a listing here does not establish current availability.
- BICC: cartridge identification reference ↗
- U.S. Army: 2010 M855 identification description, hosted by EPA ↗
- Federal · PDF pp. 58–59 ↗
- Hornady · PDF p. 183 ↗
- U.S. Army: Evolution of the M855A1 Enhanced Performance Round ↗
- U.S. Army Infantry, September–October 1988: M249 and ammunition development ↗
Diameter figures preserve the cited drawing convention. Inch–millimeter conversion uses exactly 25.4 mm per inch. Factory specifications describe the maker’s test setup; your firearm, ammunition lot, temperature, and measuring method can produce different results. This is an educational factory-ammunition reference, not a reloading manual.