Tuesday, January 3, 2012

The Evolution & Variants of the AK-47: Part I - Development History

by Mishaco (Originally posted on The Firing Range 14-Jan-2010)

This article is part of a series:
Part II - Military Variants and Accessories
Part III - Civilian Semi-Automatic Variants
Part IV - Frequently Asked Questions

Part I - Development History

Probably the single most recognizable military firearm today is the AK-47. In fact this is not a single type of rifle developed in 1947, and there after mass produced unaltered; but rather an entire family of rifles and light machineguns in several calibers. In recent years semi-automatic sporting versions of the AK have become popular in the United States. In this thread i will do my best to answer the most common questions asked and give a brief account of the development of this series.


The AK didn't spring out of the void, in fact it was designer Mikhail Kalashnikov's third design and a highly modified one at that. During the Great Patriotic War, he first attempted to win a competition to create a self-loading carbine, using an intermediate cartridge. His design went nowhere and the Soviet Union adopted the SKS-45 rifle. After the war, he sought to produce an assault rifle, after Russian troops saw first-hand the effectiveness of the German STG-44 carbine in 8mm Kurz. This second design did much better in trials and was designated AK-46. Nevertheless, improvements were suggested and a major redesign resulted in the now famous AK-47 assault rifle.

Semi-auto version of Polish WZ.1960 AK-47 type III, with early style steel slab-sided magazine.
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(Click to Enlarge)

AK-47s built between 1946 and 1948, featured a sheet steel receiver folded and welded into shape. The Type I receiver proved to be too difficult to produce for that era in Soviet Russia. As a result, in late 1948, the original receiver was replaced by a more traditional machined one, out of steel forgings. The Type II was actually more costly than the sheet steel receiver, but since Russia already had tooling and the expertise from building millions of Mosin-Nagants and thousands of SKSs, it was quicker and easier given that new machinery didn't have to be created at that time. After full scale production of the AK had begun, the 3rd and final receiver appeared. The Type III receiver was very similar to the Type II, but was machined from steel barstock. This measure decreased the cost some what and sped up the assembly process. Type II and III receivers can be told apart by differently shaped lightening cuts on each side, above the magazine; and the Type II has a lip on which the dustcover rests and the Type III does not.

The AK-47 was a selective fire assault rifle capable of either single shot or fully automatic fire. It chambered the 7.62x39 M43 cartridge, which fed from 30 round slab-sided heavy sheet steel magazines. Its barrel was 16.25" and it utilized a two-lug rotating bolt with a long-stroke gas-pistin system. The first AKs had fixed wooden buttstocks with a downward sweep, intended to compensate for muzzle climb during full-auto fire. Soon after, a version was unveiled with a metal underfolding stock, which was based on the German MP-40 submachinegun's stock. This version known as the AKS-47, was intended for airborne troops and others needing a more compact small arm. Muzzle had 14mm threads on it and came from the factory with both a muzzle nut and blank fire adapter. At this time no flash hider or compensator was issued with the AK-47. Bayonet attached on a lug directly underneath the front sight block. AK-47s produced in the 1950s featured a surprisingly high level of workmanship, fit and finish, especially those made in Russia and Poland.

Arsenal SAS M-7, a modern production AKS-47 in semi-auto by Bulgaria. Milled receiver but with new style gas-block and muzzle brake.
(Click to Enlarge)

The rifle was officially adopted in Soviet service in 1949, but due to the various changes made in the receiver and the complexity of setting up assembly lines, it was not to reach the majority of Russian soldiers until well into the 1950s. After Russia fielded the AK-47 and AKS-47, most Warsaw Pact nations followed suit, including: Bulgaria, Hungary, Poland, Romania, and East Germany. At first all nations received either completed rifles or parts to be assembled into such, from Russia; but later Poland and Bulgaria began domestic production. All of Romania's AK-47s were of Russian origin and it is unclear if Hungary ever produced whole rifles, or merely furniture and other minor components. At any rate, by the 1960s, most of East Europe was armed with Kalashnikov's rifle.


SAR-1: Civilian version of Romanian PM.63-almost an exact copy of Russian AKM, but with different handguards.
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(Click to Enlarge)

In 1959, the second generation of the rifle was announced and began being issued to Russian troops. This new design wasn't really anything new at all. The AKM's Type IV receiver was a return to the stamped steel idea with then modern manufacturing techniques. The receiver was a stamped sheet of metal folded and riveted together, with two machined trunnions at each end. The front trunnion held the barrel, gas tube and front sight base, while the rear one held the stock in place and served as a backstop for the recoiling bolt and carrier. This switch from machined receiver to stamped took 3 lbs off the total weight of the rifle. One new mechanical element of the AKM was its rate-reducer. This device was actually put into place as an out-of-battery safety, not allowing the gun to fire until the round was fully seated and the bolt closed. It also had the effect of slowing down the rifle's firing rate a bit. The AKM's furniture was lightened and scaled down slightly. The buttstock lost much of its swept angle and the pistol grip and lower handguard became slimmer. Finally, the AKM's barrel was lighter and thinner than the one found on the original AK-47. Instead of having a muzzle nut, this design most often came with a slant style muzzle brake intended to help with muzzle climb and direct gases away from the ground. This is why the stock's angle was reduced. The operating system of the new design remained the same, though magazines were changed to a ribbed style made of thinner but more durable sheet metal. The AKM could still accept older AK-47 magazines and vice-versa. The bayonet lug was shifted from the front sight base, to a new type located under the gas block. As you can see, the driving idea behind the new design was 'lighter-lighter-lighter. The AKM didn't show as high a degree of refinement as the aK-47, but nevertheless was just as reliable and durable.
The AKM proved to be even more popular than the original. In the 1960s, most East European nations began manufacturing a variant. With its light-weight and inexpensive manufacturing costs, the AKM rapidly spread around the world and was used in virtually every conflict beginning in the 1960s, through today.


AES-10B Civilian version of Romanian PM-64 which is almost an identical copy of original Russian RPK.
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The RPK is essentually an AK modified for sustained fire to fulfill the role of a light machinegun. In the 1950s, Soviet Russia was using the RPD belt-fed LMG in 7.62x39, which was both felt to be too costly to produce and unreliable. Indeed, the 7.62x39 cartridge had minimal power to operate a belt and if the gas system lost power due to fowling or poor containment the RPD could fail to cycle properly. As a result, the AKM design was upgraded to replace the RPD.

Changes from the AKM to the RPK are many. First and foremost, the barrel was made much heavier and extended to 22" long. The receiver was slightly lengthened and increased from 1.0mm thickness to 1.6mm. Likewise the dustcover was stretched and made 50% heavier. The front trunnion was bulged outwards to accommodate the heavier barrel and itself was reinforced. The rear sight was altered to allow it to be adjustable for windage via a knob on the right side, as well as still being able to be set for elevation, like on the AK-47/AKM. The RPK received new furniture with a thicker wooden handguard and a buttstock designed very much like the paddle one found on the RPD. Most recognizably, the RPK had a bipod attached just behind the front sight, which could fold under the barrel. This LMG was issued with either a 75 round top-loading drum magazine, or more commonly a set of 40 round box magazines, identical to the ones used in the AKM, only larger. Due to the longer receiver, the RPK's rate of fire was slightly lower than that of the AKM, which allowed for longer fire-sessions with fewer magazine changes and less heat build up. A side folding stock version was created for airborne troops, named the RPKS.  


ORF assembled AK-74 from Bulgarian parts on US made receiver. 
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(Click to Enlarge)

After viewing the effectiveness of the American M16 and its 5.56x45 intermediate cartridge in the Vietnam War, the Soviet Union felt it was time for a redesign of its traditional AKM rifle. Ironically it seems that the M16 earned a better reputation in Russia than it did back in its homeland. Anyway, in the 1970s work began concurrently on a new cartridge and rifle to become the new standard issue small arm in the Red Army. The 5.45x39 cartridge was created to match or out-perform the American 5.56, while still remaining the same basic length as the previous AK cartridge. This was important because it meant radical measures would not be required in the redesign of the AKM. First prototypes of the new rifle appeared in the mid-1970s, and by 1977, selected units of the Army received the very first AK-74s. The new caliber and rifle began to be issued on mass in 1979 and saw extensive service in Russia's war with Afghanistan.

Mechanically, the AK-74 is little different from the AKM. The biggest difference is of course the new caliber and smaller bore diameter. The AK-74's gas block was changed from the AKM's slanted 45 degrees gas port, to a vertical 90 degree one. This was done to reduce bullet shear. The gas block was also reinforced with brackets so a grenade launcher could be mounted underneath on a lug of the same type as the AKM's bayonet lug. Another major change was the front sight block. The AK-74's had a sleeve which covered the end of the barrel and added 24mm threads. This meant the AK-74's barrel itself was not threaded, but rather the front sight block supported the muzzle brake. The brake itself was probably the rifle's most interesting and creative aspect. It compensated for recoil by redirecting the gases backwards, as well as decreasing muzzle rise and right-drift through a series of ports. It was not; however, a flash hider. The new front sight block also supported the bayonet. Lug was located under the sight and the ring of the bayonet fit around the end of the muzzle brake.

The AK-74 originally featured wooden laminated furniture with palm swells on the handguards and lightening cuts of an ovular design on each side of its buttstock. Original butt plates were of a ribbed design with a rubber coating over metal, but quickly this changed to simply a ribbed metal plate. Handguards were reinforced with spring brackets, to insure a tighter fit and less play. The first type of magazine was of the now famous red or 'rust' color, held 30 rounds, and was made of a glass reinforced plastic. Magazines made in the 1980s, switched to a brown plastic, the better for concealment. A new feature of the 5.45 magazine was that unlike the 7.62 one, it could be loaded from 15 round stripper clips by using a special guide which fit into grooves on each side of the magazine, at its rear. The AK-74 used many of the same pins and springs as the AKM, furniture was even interchangeable. Naturally bolts, carriers, and gas pistons were not, but trigger groups were. A version of the AK-74, known as the AK-74N was produced with a side-rail mount, intended for the addition of night optics.

The first variant of the AK-74 to appear was the AKS-74. This was simply a standard rifle, which had a side folding stock and new rear trunnion, instead of the traditional fixed stock and trunnion. The stock was made from stamped and folded steel of a triangular shape. It folded to the left side and when folded was locked in place with a strong spring-loaded hook. When opened the stock was also held firmly in place by another large spring-loaded catch. These rifles were designed for airborne units and replaced the AKMS. They were felt to have a stronger and more durable folding stock.

Arsenal built clone of the AKSU, with polymer handguards.
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(Click to Enlarge)

The AKS-74U was the next variant of the AK-74 to appear and it was a much more extensive modification of the original design. First, the stock from the AKS-74 and rear trunion were taken. Then the barrel was shortened from 16.25" to just under 8.5". This meant the entire gas system had to be shortened accordingly. The gas block and front sight block were combined into a single unit to conserve space and the handguards also had to be shortened. The rear sight was changed to a flip-style with two settings and was moved back to be on top of the dustcover. The dustcover itself was also redesigned to have a henge at the front so that during disassembly, instead of being removed, it was simply folded forward. When dustcover was open like a car hood, a spring-loaded pin retracted, allowing the gas tube to be lifted off. Finally, the AKS-74U had a new muzzle device, on the same 24mm threads. This was a conical flash hider combined with a gas-expansion chamber, which was necessary to insure reliable cycling with such a short barrel. This carbine could not accept a bayonet and took a specialized sling as well. It was primarily intended for special operations forces and mechanized units, but also was sometimes requested by airborn troops. It was extremely small and easy to handle, but for these attributes, it traded range and had a tendency to overheat. Nevertheless, the AKS-74U was popular among certain circles as it was an intermediate step between an assault rifle and submachinegun - very similar to the role the Colt CAR-15/XM-177 filled.

Zastava M92 AKSU, built into a pistol. It has no buttstock and a 9.5" barrel.
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(Click to Enlarge)

The RPK was also re-chambered for the new 5.45x39 cartridge and renamed the RPK-74. This new model was very similar to the original LMG but instead of having a muzzle nut on its 14mm threads, it had a 5 slot birdcage flash hider. An RPKS-74 appeared at the same time. This model used 45 round magazines. First generation ones were made of the same reddish plastic as the AK-74's and later generations were black or plum polymer. No drum was ever mass produced. Overall though, the new RPK was the same as the original.

AK-74M & the Century Series

In the 1980s, Russia turned its attention to developing a new line of AKs, intended for the World market. They took their AKS-74 and began modernizing and upgrading it. Furniture was changed to rugged polymer and buttstock became a solid body style that could still fold just like the one on the AKS-74. This new stock could even house a cleaning kit, a feature previously only available on fixed stocked models. Next, the side-rail mount became standard on all rifles and magazines were made of polymer with metal reinforcement in a 'waffle' pattern. The muzzle brake was also changed to both be more effective and cheaper to produce. Dustcovers were changed from a ribbed style to a smooth style, at least on some models. Many other small changes also occurred both in design and manufacturing techniques. This new generation became known as the AK-74M. 

At the same time, the RPK-74 also received a facelift. Its laminated furniture was changed to the same black or plum polymer style as the AK-74M and its magazines were made from black polymer. This new model became known as the RPK-74M and came standard with a side-rail mount.
Russia released an AK-74M chambered in 5.56 NATO for commercial sales designated the AK-101. Next out the door was the AK-103, the same design but in 7.62x39 M43. This model was both for world sales and was requested by certain groups inside Russia, who felt the 5.45 caliber was not best suited for their needs.

Bulgarian RPK-74M parts kit built on US receiver with modern magazine and LMG sling.
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(Click to Enlarge)

To replace the AKS-74U and address some of its issues, the AK-102/104/105 carbine series was developed. These were of the same class weapon as the later Colt M-4 carbine. This series has a 12" barrel, conical style flash hider, combination front sight and gas block; but retains a standard length gas system and sight picture. AK-102 = 5.56 NATO, AK-104 = 7.62x39, and AK-105 = 5.45x39. All versions are in production today, along with the AK-74M, which is now the Russian federation's general issue small arm. The most recent AK designs are the AK-107 and AK-108. These have a counter-weight system to cancel out most felt recoil during automatic fire, but have not been adopted by any military in large numbers yet. 

Arsenal SLR-106CR with removable muzzle device and 'smoke' waffle magazine of 30 rounds.
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(Click to Enlarge)

And there you have a brief history of the AK as a military firearm. 

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