5.45 x 39 mm M74

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sectional drawing of a cartridge 5.45x39 mm (Kalashnikov AK-74)
A:projectile jacket; B:steel core; C:hollow point; D:lead inlay; E:propelling charge

The Soviet 5.45 × 39 mm M74 round was introduced into service in 1974 for the AKSU-74 carbine/sub-machine gun and the AK-74 assault rifle, which is an updated version of the AK-47. The round, which replaced the AK-47's 7.62 x 39 mm round then in Soviet service, was likely developed based on Soviet observation of the American 5.56 x 45 mm NATO round in Vietnam.

The Russian military-issue 5N7-specification 5.45 mm bullets are a somewhat complex full metal jacket design. Some people have said that the Russians were concerned about the lower energies of the bullets and designed them to cause more damage than might otherwise occur. The bullet's core consists mainly of a length of soft steel rod, cut to length during the manufacturing process to give the correct weight. There is a hollow air space underneath the bullet's thin copper jacket ahead of the steel rod core. The base of the bullet is tapered, to reduce vacuum drag (a so-called boat-tail bullet) and there is a small lead plug crimped in place in the base of the bullet, ostensibly so that the thin copper alloy jacket material can be stamped in place in the proper tapered shape. The lead plug, however, in combination with that air bubble in the point of the bullet, has the effect of pushing the bullet's center of gravity very far to the rear, and the hollow air space under the point of the bullet makes the bullet's point prone to bending to one side when the bullet strikes anything solid, unbalancing it. Some Western authorities believed this bullet was designed to tumble in flesh to increase wounding potential.

At the time, it was mistakenly believed that yawing and cavitation of projectiles was of major importance in producing tissue damage. Although Dr. Martin Fackler later showed that projectile fragmentation was the key to producing significant wounding effect; this was unknown to the Soviets when they began development of the new round. This was similarly unknown to the non-Soviet alarmists who feared that they had achieved wounding parity with the 5.56 x 45 mm round used in the West's M16 rifle.

However, the rigidity of the 5.45 bullet prevents fragmentation and gave it a reputation for being a mediocre stopper. Reports of the 5.45 projectile producing horrific wounds have been repeatedly demonstrated to be false. In his terminal ballistics study using live pigs and ballistic gelatin (1984), Fackler was able to demonstrate that the AK-74, even at close range, did no more damage than a handgun round. The only exception was a hit to the liver, which caused heavy damage due to the stiffness of the organ. All other organs and tissue were too flexible to be severely damaged by the temporary stretch effect.

With the 5.45 mm bullet, the tumbling produced a temporary stretch cavity twice, at 100 and 400 mm of depth. This is comparable to modern 7.62 x 39 mm ammunition and to tungsten penetrator (non fragmenting) 5.56 ammunition. The average width of a human trunk is 400 mm.