545x39mm

The 5.45×39mm cartridge, commonly written as 5.45x39mm and sometimes referred to as 545x39mm, is a Soviet-origin rifle ammunition developed in the 1970s for the AK-74 family. It was designed as a lighter, higher-velocity alternative to the 7.62×39mm while preserving effective range and penetration, particularly in automatic fire.

Design and characteristics: The cartridge uses a bottleneck, rimless case with a small-diameter bullet, typically around 5.6 mm. The standard military load features a lead or steel-core bullet with a full metal jacket; armor-piercing and tracer variants are also produced. Typical muzzle velocity for common ball rounds is in the vicinity of 850–930 m/s, with corresponding energy around 1.1–1.3 kJ. The higher velocity contributes to a flatter trajectory and reduced recoil compared with larger calibers.

Service and use: The 5.45×39mm entered service with the AK-74 in the early 1970s and gradually became the primary cartridge for Soviet and later Russian infantry, replacing much of the 7.62×39mm in standard-issue rifles. It remains in use in Russia and many post-Soviet states, and has been exported for various military and commercial applications.

Variants and performance: Ball ammunition provides standard performance for general use, while armor-piercing rounds rely on a hardened core for penetration against lightly protected targets. Tracer variants exist to aid fire adjustment in low-light conditions.

See also: 5.56×45mm NATO, 7.62×39mm.