The Soviet 5.45 × 39 mm round was introduced into service in 1974 in the AK-74 assault rifle, an updated version of the AK-47. The round, which replaced the 7.62 × 39 mm round then in Soviet service, was likely developed based on Soviet observation of the American 5.56 × 45 mm 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. Most authorities in the West believe this bullet is designed specifically to tumble in flesh, tremendously increasing the severity of the wound.

When shot into 10% ballistic gelatin at 4°C (the standard simulant for human flesh, in the field of ballistics), the bullets always begin to tumble, sometimes less than 2" (5 cm) from the point of entry, and usually tumble end over end two or three times before coming to rest at a depth of 12" to 16" of penetration (30cm to 40cm); it may also move in a curved or even zig-zag path through the gelatin block as it tumbles. In combat in Afghanistan in the 1980s, and since that time, the 5N7 bullet has earned a fearsome reputation for creating horrific wounds.

With the 5.45 mm bullet, the tumbling produced a maximum wound expansion twice, at 100 and 400 mm of depth. With the 7.62 mm bullet, the maximum wound expansion also occurred twice, at about 300 and 400 mm. The average width of a human trunk is 400 mm.