Firearms Technical Trivia, October 2001:

Soviet Flag
A Brief Look at the 5.45x39mm Cartridge
Russian Flag

The Russian interest in reduced caliber cartridges for infantry rifles can be traced back to the early 20th century, with the development and issue of the Fedorov M1916 Avtomat.  Chambered for the 6.5x50mmSR Japanese service cartridge, the M1916 represented the start of a trend away from conventional full power service rifle cartridges that was to be the hallmark of Russian and Soviet ammunition development through much of the 20th century.  After the ravages of the First World War and the subsequent civil war between white and red forces that forged the Soviet State, reduced caliber cartridge development was resumed and continued until the Second World War forced a reallocation of effort and resources.

However, it was not until the American military transitioned to the M16 rifle and its 5.56x45mm cartridge in the 1960's that serious development efforts aimed at creating a small-bore cartridge to supersede the 7.62x39mm cartridge began.  The result was the 5.45x39mm cartridge, or 7N6, the advent of which was an event of

7N6 - 5.45x39mm Ball Cartridge
7N6 5.45x39mm Ball Cartridge
critical importance to the European military scene.  One one level it represented strong  conservative bent typical of Russian and Soviet military thinking:  the adoption of the 5.45mm round permitted the Soviet and Warsaw Pact forces to improve their basic infantry weapons without eliminating the technological base upon which the older generation was grounded.  On another level it was a radical change:  After a quarter century of cartridge standardization within the Warsaw Pact, the Soviet Army took the decision to replace their 7.62x39mm arms - millions of AKM's and RPK's - with new versions firing the 5.45mm round.  Accordingly, the first reports of the new cartridge befuddled western intelligence analysts who made the assumption that the new small caliber rifles and machine guns would be used only by specialized units.  They simply could not believe that the changeover would be a one for one replacement of existing stocks of 
rifles and squad automatic weapons because of the logistical problems inherent to such a switch.  The fact that the Soviets were able to update their arsenal with 5.45mm weapons indicated that their industrial sector was far more advanced than previously estimated.

The 5.45mm family of cartridges comprises:

Modernized Tracer
Reduced Velocity

The cartridges were designed by a "dream team" of modern Soviet small arms designers headed by Viktor Sabelnikov and including Lidiya Bulavskaya, Boris Semin, Mikhail Fedorov, Petr Sazonov and Petr Korolev.  The basic characteristics of the 7N6 ball cartridge are:

Cartridge Weight:
157.41 grains
Bullet Weight:
52.47 grains
Propellant Weight:
22.38 grains
Overall Length:
Case Length:
Case Type:
Rimless, bottlenecked
Bullet Length:
Propellant Volume:
1.56 cc
Maximum Chamber Pressure:
3,000kg/cm2 (42,670 psi)

The small caliber bullet matches high muzzle velocity with excellent sectional density, resulting in a flat trajectory and good penetration.  Indeed, the standard ball cartridge will penetrate 5mm of steel plate at a distance of 350 meters.  Additionally, the lowered recoil impulse of the 5.45mm cartridge (vice the 7.62x39mm) had a beneficial effect on accuracy, increasing the fire efficiency of the AK74 some 40 percent on average over the AKM.

The 5.45mm cartridge remains the least powerful military rifle cartridge in general use.  With a muzzle velocity of 900 meters per second, it is significantly slower than the NATO standard M855/SS109 5.56x45mm cartridge.  Similarly, the 5.45mm round, at 1,008 foot pounds, has less muzzle energy than the M855, which can boast 1,325 foot pounds.  It also has fifteen percent less case capacity than the 5.56mm cartridge (and twenty-nine percent less case capacity than the 7.62x39mm).  The 5.45x39mm overcomes these apparent statistical shortcomings

in a number of ways.  To begin with, the bullet is not seated as deeply as in the 5.56mm cartridges.  Next, by using a shorter, fatter case, the 5.45mm's bullet could be designed such that it was ballistically efficient, but still relatively short.  Additionally the case shape makes for significantly more efficient combustion that is possible with the 5.56mm's longer, narrow case.  Indeed, the 5.45mm's 3,000 fps muzzle velocity is achieved with a chamber pressure that is almost twenty percent lower than that of the 5.56mm.  Finally, the 5.45mm uses an advanced, very efficient propellant, with a combustion rate matched very 
5.45mm Ball Projectile
closely to the cartridge characteristics.  The powder composition is 81 percent virgin nitrocellulose base material, 11.6 percent nitroglycerine, 5.3 percent ethyl centralite, 0.9 percent dinitrotoluene as a stabilizer, and 0.4 percent undefined organics.

While the 5.45mm's high velocity made for a flatter trajectory, and easier range estimation, there were initial questions as to the 5.45mm's lethality.  These later proved to be unfounded, as the 5.45mm projectile is designed and constructed very carefully so as to maximize lethality base on the cartridge characteristics.  (As an aside, western intelligence agencies initially postulated that there might be a higher velocity 5.45mm cartridge for war usage.  As the initial samples were taken from the Afghan campaign, this was unlikely at the time, and has since been disproven.)  The AK74 rifle has a 16.3" barrel with a rifling twist of 1:9.25", which results in a very rapidly spinning bullet (approximately 233,513 rpm).  As a result, the projectile is extremely stable as it flies through the air.  That stability comes to a violent end as soon as the projectile enters a medium that is more dense than air.

5.45mm Projectile Cross Section
The basic  ball projectile (Russian military nomenclature 7N6) has a gilding metal clad mild steel jacket.  Inside the jacket is a lead sheath, which in turn surrounds a 15mm long mild-steel core.  The mild steel core's base is mounted at the base of the bullet jacket.  At the steel core's nose is a 3mm long lead plug which is actually an extension of the lead sheath.  In front of the lead plug is an air space approximately 5mm long.  By placing the projectile's center of gravity toward the rear, the design team virtually ensured that it would tumble end over end when it struck a human body:  When the bullet strikes a target hard enough to deform its nose, the hollow cavity is crushed, and the center of gravity changes rapidly, causing the projectile to upset and tumble.  Once 
the bullet has begun to tumble, it quickly transfers its kinetic energy into the target, thus bringing the maximum wounding force to the target.
5.45x39mm Core Displacement Upon Firing
A roentgenogram showing ten consecutive fired bullets (flanked by two unfired ones for comparison) to illustrate that the core shift does in fact occur, and creates an asymmetrical bullet.
Image credit:  Ezell, Edward C., The AK47 Story, (Stackpole Books, Harrisburg, Pennsylvania: 1986) Page 243
This gains in importance when one recalls that lethality is the product of the amount of energy deposited into the target over time.  Bullets such as the full power 7.62mm NATO tend to be less lethal than the smaller, high velocity projectiles, because such bullets tend to punch neat holes into and out of their targets, thus not depositing much energy as as projectile that stops within the target.
5.45mm Wound Profile
5.45mm Wound Profile - Note extreme depth of wound and dual cavities
5.56mm Wound Profile
While occasionally given short shrift by American shooters and writers enamored with the 5.56x45mm, the 5.45x39mm cartridge is an excellent round that offers comparable penetration, accuracy and lethality to anything fielded by a NATO nation.  It's also a historically fascinating cartridge.  Indeed, a strong case can be made that the 7N6's lineal ancestor is not Russian at all, but rather British.  The British  Mk.VII .303 ball cartridge featured a bullet with either an airspace or lightweight kapok filler at the nose that was designed to tumble upon impact with the target.  It is more than likely that the Soviet team took a page from the British book when designing the 7N6.  And in a very timely manner, the 7N6 has come full circle:  A cartridge first tested in an Afghan war, designed with the experience of another Afghan war in mind, may very well become the lingua franca of a third Afghan war.

Note: Data for this month's trivia page was gathered from:

Barnes, Frank C., Cartridges of the World, 8th Edition, (DBI Books, Northbrook, Illinois: 1997)

Cartridges of the World is available from IDSA Books.  Click on the image to order.
Cartridges of the World

Bolotin, D.N., Soviet Small Arms and Ammunition, (Finnish Arms Museum Foundation, Hyvinkaa, Finland: 1995)

Soviet Small Arms and Ammunition is available from IDSA Books.  Click on the image to order.
Soviet Small Arms and Ammunition

Ezell, Edward C., The AK47 Story, (Stackpole Books, Harrisburg, Pennsylvania: 1986)

Kalashnikov:  The Arms and the Man, an updated version of The AK47 Story, is available from Collector Grade Publications.  Click on the image to order.
AK-47 Story

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