5.56 × 45 mm NATO
Standard NATO assault rifle cartridge
The 5.56 × 45 mm NATO is the second NATO standard rifle cartridge, standardised under STANAG 4172 in October 1980. Its light recoil allows a soldier to carry far more rounds for the same weight and to control automatic fire, and the SS109/M855 steel-penetrator projectile will defeat up to 3 mm of steel at 600 m. It is the principal chambering for the assault rifles, carbines and light machine guns in Steadfast’s small arms division.
Full Specifications
Cartridge dimensions
| Designation | 5.56 × 45 mm NATO (SS109 / M855, M193) |
|---|---|
| Case type | Rimless, tapered bottleneck |
| Bullet diameter | 5.70 mm (0.224 in) |
| Neck diameter | 6.43 mm (0.253 in) |
| Shoulder diameter | 9.00 mm (0.354 in) |
| Base diameter | 9.58 mm (0.377 in) |
| Rim diameter | 9.60 mm (0.378 in) |
| Case length | 44.70 mm (1.760 in) |
| Overall length | 57.40 mm (2.260 in) |
| Case capacity | 1.85 cm³ (28.5 gr H₂O) |
Ballistics
| 55 gr (3.56 g) FMJBT | 993 m/s (3,260 ft/s), 1,755 J |
|---|---|
| 62 gr (4 g) SS109 / M855 | 948 m/s (3,110 ft/s), 1,797 J |
| 62 gr (4 g) M855A1 | 961 m/s (3,150 ft/s), 1,847 J |
| Test barrel length | 508 mm (20 in) |
| Rifling twist | 178 mm (1 in 7 in) or 229 mm (1 in 9 in), six grooves RH |
Standards & pressure
| NATO / C.I.P. Pmax | 430.00 MPa (62,366 psi); proof 537.5 MPa |
|---|---|
| NATO piezo service pressure | 420.0 MPa (60,916 psi) |
| Primer | Small rifle |
| Standardisation | STANAG 4172, standardised 28 October 1980 |
| Chambering caution | Do not fire 5.56 NATO in rifles chambered for .223 Remington |
Service context
| Introduced | Developed late 1970s by FN Herstal, Belgium |
|---|---|
| Effective range | 500 m point target from a carbine; 600 m area target |
| Penetration | 3 mm steel at 600 m (SS109); 12 mm RHA at 100 m (tungsten core) |
| Typical platforms | Assault rifles, carbines, DMRs and light machine guns |
Dimensional, ballistic and pressure figures are the published C.I.P., NATO and SAAMI reference values for the 5.56 × 45 mm NATO cartridge (reference data; ANSI/SAAMI Z299.4 centerfire rifle standard). Steadfast production lots are proof tested and certified against the applicable standard. Product imagery is an in-house Steadfast studio visualisation and is indicative only; actual finish, headstamp and lot markings follow the applicable standard and the customer order.
