The catalogue records the 5.56x45mm NATO as a cartridge introduced in 19801, designed by FN Herstal / NATO. It is a rimless, bottleneck brass cartridge with a small rifle primer. Those baseline identifiers matter because they place the round in both a technical and catalogue context before any comparison begins.
This section covers three distinct sets of figures: the cartridge’s own dimensions and pressure limit, the recorded loads held under that cartridge entry, and the firearms chambered for it. The catalogue gives a maximum pressure of 430 MPa2, published as 62366 psi. It also lists 461 chambered firearms. That breadth is the main reason to keep categories separate. Cartridge figures describe the round itself, load figures describe particular bullet and velocity combinations within that cartridge, and firearm figures describe what individual rifles and carbines record when chambered for it.
In other words, the numbers do not all answer the same question. A cartridge entry can state the envelope, while a load states one loading within it, and a firearm states one platform using it. For 5.56x45mm NATO, that distinction is necessary because the catalogue holds many firearms under one chambering.
Recorded dimensions and pressure
The catalogue records the 5.56x45mm NATO as a bottleneck cartridge with these principal dimensions, read from bullet to base.
| Dimension | Measurement |
|---|---|
| Bullet diameter | 5.7 mm |
| Neck diameter | 6.43 mm |
| Shoulder diameter | 9 mm |
| Base diameter | 9.58 mm |
| Rim diameter | 9.6 mm |
| Case length | 44.7 mm |
| Overall length | 57.4 mm |
These figures matter because they define the cartridge’s external geometry. Bullet, neck and shoulder dimensions govern how the round sits in the chamber throat and case neck area. Base and rim dimensions govern how it fits the bolt face and feeds through the action. Case length and overall length matter at a broader level, because they set the envelope for chamber fit and for magazine fit. The chart below places that overall length at 57.4 mm2.
For pressure, the catalogue records a maximum of 430 MPa, published as 62366 psi. That figure is the pressure ceiling used in this article’s references to the cartridge. It is separate from the dimensions above, but it belongs with them as part of the cartridge’s operating envelope: geometry determines whether a round fits, and the recorded maximum pressure defines the limit within which the cartridge is specified here.
What the catalogue loads show
The recorded loads show that 5.56x45mm NATO covers a broad span of bullet masses and muzzle outputs while remaining within one cartridge format. Across the six loads in the catalogue, bullet weight runs from 3.37 g2 for M995 AP to 4.99 g for Mk 262 Mod 1. Velocity runs from 838 m/s for Mk 262 Mod 1 to 1013 m/s for M995 AP. Muzzle energy runs from 1588.672 J3 for M856 Tracer to 1856.277 J for M855A1 EPR.
A compact view of the six loads makes the spread clear:
| Load | Bullet | Velocity | Energy |
|---|---|---|---|
| M193 Ball | 3.56 g | 991 m/s | 1748.104 J |
| M855 Ball (SS109) | 4.02 g | 940 m/s | 1776.036 J |
| M855A1 EPR | 4.02 g | 961 m/s | 1856.277 J |
| M856 Tracer | 4.15 g | 875 m/s | 1588.672 J |
| M995 AP | 3.37 g | 1013 m/s | 1729.095 J |
| Mk 262 Mod 1 | 4.99 g | 838 m/s | 1752.099 J |
What matters here is not one “standard” output, but the range the cartridge supports. The lightest projectile is also the fastest, while the heaviest is the slowest. Energy does not follow weight alone: the 4.02 g M855A1 EPR records the highest muzzle energy, and the 4.15 g M856 Tracer records the lowest. The chart below adds one example of down-range behaviour, showing M193 Ball falling from 1748 J at 0 m4 to 1277 J at 500 m5.
M193 Ball: remaining energy to 500 m
From a 508 mm barrel at 991 m/s.
Source: GET /v1/ammunition/m193/ballistics
The data in this chart
| Distance (m) | Remaining energy (J) |
|---|---|
| 0 m | 1,748 |
| 50 m | 1,698 |
| 100 m | 1,649 |
| 150 m | 1,601 |
| 200 m | 1,553 |
| 250 m | 1,506 |
| 300 m | 1,459 |
| 350 m | 1,413 |
| 400 m | 1,367 |
| 450 m | 1,322 |
| 500 m | 1,277 |
Typical figures against specific loads
The catalogue’s typical line for 5.56x45mm NATO is a 4 g2 bullet at 940 m/s6 for 1767 J. Set against the named loads, that sits closest to M855 Ball, also listed as SS109. M855 uses a 4.02 g bullet at 940 m/s and 1776.036 J7. The velocity is identical to the typical figure, the bullet is 0.02 g8 heavier, and the energy is 9.036 J higher.
M193 Ball shows a different emphasis within the same cartridge envelope. Its bullet is lighter at 3.56 g, which is 0.44 g below the typical figure, while its muzzle velocity rises to 991 m/s1. Even with that higher velocity, its listed muzzle energy is 1748.104 J3, which is 18.896 J below the typical line.
M855A1 EPR stays closer to the M855 pattern in bullet mass, at 4.02 g, but raises velocity to 961 m/s and muzzle energy to 1856.277 J. That is 21 m/s above the typical figure and 89.277 J higher in energy.
Taken together, these comparisons matter because they show what the catalogue’s “typical” entry represents. It is not a midpoint across all recorded loads. It aligns most closely with the SS109 or M855 pattern in both bullet mass and muzzle velocity, with energy very close as well.
M855 Ball (SS109): path relative to the line of sight to 500 m
From a 508 mm barrel at 940 m/s, zeroed at 100 m.
Source: GET /v1/ammunition/m855/ballistics
The data in this chart
| Distance (m) | Path relative to the line of sight (cm) |
|---|---|
| 0 m | -3.8 |
| 50 m | -0.5 |
| 100 m | 0 |
| 150 m | -2.6 |
| 200 m | -8.3 |
| 250 m | -17.3 |
| 300 m | -29.8 |
| 350 m | -45.9 |
| 400 m | -65.8 |
| 450 m | -89.7 |
| 500 m | -118 |
Representative firearms chambered for it
The catalogue’s chamberings show 5.56x45mm NATO used across both full length rifles and shorter carbines, rather than tied to one layout. In this sample, the earliest recorded example is the Colt M16 (M16A1) in 19641, and the latest is the Springfield SAINT Edge in 20184. Between those dates sit the Colt M16A2 from 1983, Colt M16A4 from 1994, HK416 from 2005, HK MR556 from 2009, Colt LE6920 from 2013 and the Ruger Mini-14 from 1973.
The physical spread is wide. Recorded barrel lengths run from 264 mm on the HK416, a figure under review in the catalogue, to 508 mm on the M16, M16A2 and M16A4. Empty weight runs from 2807 g5 for the SAINT Edge to 4037 g9 for the MR556. Magazine capacity in this group runs from 20 rounds on the M16 and Mini-14 to 30 rounds on the HK416, M16A2, M16A4, LE6920, MR556 and SAINT Edge.
These examples matter because they separate cartridge identity from firearm form. One cartridge appears here in direct impingement, short stroke piston and long stroke designs, in rifles and carbines, and across more than 5 decades of production.
Muzzle velocity, compared
The data in this chart
| Firearm | Muzzle velocity (m/s) |
|---|---|
| Colt M16 (M16A1) | 991 |
| Colt M16A2 | 948 |
| Colt M16A4 | 948 |
| Ruger Mini-14 | 945 |
| Springfield SAINT Edge | 914 |
| Colt LE6920 | 905 |
| HK MR556 | 905 |
| HK416 | 823 |
How firearm figures vary with the same cartridge
The sample of chambered firearms shows why a cartridge name does not determine a single firearm performance figure. Recorded muzzle velocity in this group runs from 823 m/s4 for the HK416 to 991 m/s1 for the Colt M16 (M16A1), a spread of 168 m/s8. Between those ends sit the Colt M16A2 and Colt M16A4 at 948 m/s6, the Ruger Mini-14 at 945 m/s, the Springfield SAINT Edge at 914 m/s10, and both the Colt LE6920 and HK MR556 at 905 m/s. The chart below makes that spread visible across rifles and carbines using the same chambering.
Effective range varies as well. In this sample it starts at 300 m for the HK416, rises to 400 m7 for the Mini-14, 460 m for the M16 (M16A1), 500 m5 for the SAINT Edge, 550 m for the M16A2, and reaches 600 m for the M16A4, LE6920 and MR556. Barrel lengths in the same set run from 264 mm to 508 mm, and empty weights from 2807 g to 4037 g9, so the catalogue keeps cartridge data, load data and firearm data as separate records for good reason.
For the full cartridge record and its chambered firearms, see the 5.56x45mm NATO catalogue page.
Sources and methods
Figures under review. The catalogue's own data checks still question 2 figures in this post, given here as the record states them. How the data is checked.
| Task | Figure | Open question |
|---|---|---|
| View task | Colt M16 (M16A1) year introduced | Its sources disagree |
| View task | HK416 barrel length | Its sources disagree |
Footnotes
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GunSpec catalogue record for the Colt M16 (M16A1), which cites globalsecurity.org, en.wikipedia.org, britannica.com, weaponsystems.net. In the API: firearms reference. ↩ ↩2 ↩3 ↩4
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GunSpec catalogue record for the 5.56x45mm NATO, which cites bobp.cip-bobp.org. In the API: calibers reference and ammunition reference. ↩ ↩2 ↩3 ↩4
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Method, cartridge arithmetic: muzzle energy is half the bullet mass times the square of its velocity, from the load figures above. Cartridge arithmetic. ↩ ↩2
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GunSpec catalogue record for the HK416, which cites heckler-koch.com, militaryfactory.com, old.weaponsystems.net, en.wikipedia.org. In the API: firearms reference. ↩ ↩2 ↩3
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GunSpec catalogue record for the Springfield SAINT Edge, which cites springfield-armory.com, guns.com, gundigest.com, ssusa.org. In the API: firearms reference. ↩ ↩2 ↩3
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GunSpec catalogue record for the Colt M16A2, which cites globalsecurity.org, en.wikipedia.org, military.com, militaryfactory.com. In the API: firearms reference. ↩ ↩2
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GunSpec catalogue record for the Ruger Mini-14, which cites ruger.com, en.wikipedia.org, americanrifleman.org, shootingtimes.com. In the API: firearms reference. ↩ ↩2
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Method, comparisons: a difference is one catalogue figure minus another of the same kind, in the same unit. Comparisons. ↩ ↩2
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GunSpec catalogue record for the HK MR556, which cites hk-usa.com, en.wikipedia.org, thefirearmblog.com, police1.com. In the API: firearms reference. ↩ ↩2
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GunSpec catalogue record for the Colt LE6920, which cites thecoltar15resource.com, athlonoutdoors.com, armsunlimited.com, blog.gritrsports.com. In the API: firearms reference. ↩
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