KALASHNIKOV: The AK-47 & AKM Rifles, Part 1 of 2
By Frank Iannamico
This article focuses on comparing the milled receiver 7.62x39mm AK (47), the 1959 AKM and the 5.45x39mm AK-74. The 7.62 AK was first issued in 1949, the AKM in 1959 and the AK-74 in 1976.
In the case of the 7.62mm AK, there were at least two variations produced and issued before a final version was manufactured in large numbers and the technical data package shared with the Soviet’s satellite nations. The AK was manufactured by 20 known countries.
The first production model of the AK had a stamped-riveted receiver, which for reference in the West is known as the Type 1. Apparently, there were production problems encountered with the stamped receiver AK, as a short time after its introduction a second model AK appeared, known in the West as the Type 2, with a forged steel-machined receiver followed by the forged receiver Type 3 a few years later. The particular problems with the original stamped AK receiver are not known. But a second stamped receiver AK, the 7.62 AKM, didn’t appear until 1959.
U.S. Technical Report, U.S. Army Weapons Command Research & Engineering Directorate Small Arms Systems Laboratory Analysis of the Soviet AK-47 Rifle, 1968 The Soviet 7.62mm Model AK-47 is a magazine fed, percussion fired, gas operated, semi/full automatic weapon. In its geometry, it has a slight drop stock, pistol grip, with the gas piston located above the barrel, ramp-type open sights, with a battle range setting of 300 meters and mid-height front sight.
The thirty-round magazine curves forward to suit the accumulated taper of thirty cartridges and extends approximately 7.0-inches below the receiver.
The breech mechanism consists of a rotating bolt, actuated by a reciprocating bolt carrier. The bolt carrier rides in keyways in the receiver. An internal cam is machined in the forward section of the bolt carrier and rotates the bolt during the locking and unlocking phases of the cycle. Two locking lugs are positioned at the front of the bolt and are diametrically opposed. The lock cam lug is mounted on the outside periphery of one of the bolt lugs, increasing the momentum for a favorable cam force leverage. Noted is the highly favorable mass ratio (5:1) between the bolt carrier and bolt.
A slender cylindrical section of the bolt body is supported in the bolt carrier. The bolt also contains a free-floating firing pin and an extremely simple cylindrical extractor.
A single drive spring, mounted on a telescoping guide rod, drives the bolt carrier assembly in counter-recoil. The guide rod base also functions as a cover latch; therefore, the spring serves double duty. Also, when the spring assembly unit is removed, it remains as an easily handled subassembly. The receiver housing cover may be removed and the weapon function, for visual inspection of the operating mechanism, may be studied.
The gas system is the plain impingement system, with the piston being part of the bolt carrier. The piston end is concave, as is the end of the gas piston housing. This provides an initial chamber volume. The upper handguard is also the gas piston housing, with gas bleed holes incorporated in the gas cylinder extension. A single gas orifice is used, with no adjustment for power necessary. The gas piston housing tube is ribbed for rigidity, and the operating rod is easily accessible.
The receiver also functions as the firing mechanism housing assembly. The firing mechanism has eleven parts, including three retaining pins. The automatic sear spring has a single long arm that groove-locks these pins. Three sears are used in the mechanism with a double claw hammer for the primary and secondary sears, and a single (hammer hub) notch for the automatic sear, actuated by the operating rod. The primary and secondary sears are identical to the M1 rifle in principle. When the hammer is in battery, the safety can be applied. This would cause a jam when attempting to charge the weapon. However, the charging slot closure is a good visual indicator that the safety is on. The selector shaft controls the functioning of the semiautomatic sear and trigger.
The front sight is a hooded post, which can be adjusted by using the combination tool provided in the tool kit, either by screwing it up or down or moving it left or right. The rear sight is the conventional V-notch tangent leaf, the sight radius being approximately 15-inches. The upper forearm is retained by a latch on the rear sight. When the upper forearm is removed, a latch for the lower forearm is revealed. The lower forearm conceals a hiding pocket in the receiver.
The AK-47 will group in 6-inches at 100 yards. In full-automatic, the weapon climbs rapidly, when firing bursts of five or more rounds. The AK’s accuracy is not up to U.S. standards; this was attributed to the AK’s poor human engineering; a short sight radius, short stock, and high line of recoil. In another test, the AK was evaluated to see how effective the weapon would be in combat. The test was conducted with a proficient marksman, equipped with a basic combat load of four magazines. The shooter followed Soviet military tactics of firing three to five shot bursts, followed by a three to four second pause to reacquire the target, or change out an empty magazine. The average time was 110 to 115 seconds, but after the magazines were emptied evaluators found that it was very time consuming to reload the magazines by hand. The M16 held a significant advantage in this respect, with its stripper clip magazine reloading system. (A similar stripper clip system was later adopted by the Russians for the AK-74.)
The weapon fires from the closed bolt position for either semiautomatic or full-automatic cycles of operation. There is no bolt hold-open device to hold the action open after the last round in the magazine is fired.
The AK-47 will eventually be replaced by the AKM a modification that is characterized principally by a sheet metal rather than a milled receiver, as well as several other changes.
T7.62X39MM Magazines
The curved magazine tube is made of heavy gauge spot-welded construction with critical areas, such as the feed lips and catches being machined. The magazine follower is a stamping, with a long skirt to control tipping, by its close fit with the inside wall of the magazine.
The magazine contains a number of highly desirable design features. The extremely rugged magazine lips are most favorable for extended field use. The magazine follower does not have to be critically balanced between the ammunition stack and the follower spring. No matter where one bears down on the follower (the center, forward or rearward position), the follower moves in the magazine smoothly. The spring design, therefore, can be simple oval coils, free of stress concentrations, and free from binding along the magazine ribs. The magazine follower design along with the 5:1 mass ratio between the bolt carrier/bolt are the two reasons why this weapon continues to fire in the field with old, corroded, apparently unusable ammunition.
A hole at the lower rear surface of the magazine tube is an excellent visual indicator that the magazine is full. The user merely adds rounds until the bottom round shows up in the hole.
A three-piece tool kit is stored in the buttstock, with a spring based pressure plate facilitating entry and removal. The kit contains a combination tool, bore brush, and a cleaning patch jag. The combination tool provides a screwdriver blade, punch, and two wrenches. The cleaning rod is stored under the barrel, and through the lower handguard. The body of the tool kit is a handle and the end cap attached to the muzzle as a guide for the cleaning rod.
Weapon field-stripping is accomplished without tools, by a system of guide slots in the receiver, for the operating rod and retaining latches for the upper and lower handguards.
The barrel is rifled with four lands and grooves, with a right-hand twist. The muzzle attachment nut is threaded left-hand. The gas port is at an angle, which simplifies cleaning. No parts other than the gas piston and upper forearm are removed for this bit of maintenance. Training in weapon maintenance is considered to be fairly simple. While not convenient for bayonet fighting, the short weapon length is handy for street and house-to-house fighting. The basic weapon is also equipped with a folding buttstock, for paratroopers and special services.
An estimate of cost production was made in 1968, and based on a quantity of a lot of two-million rifles, the weapon would cost approximately $60 without production engineering or final inspection services. Also, it was estimated that approximately 550 machine operations are necessary as opposed to the 800 for the M14 rifle. The weapon was made almost entirely from milled steel components, along with a few stampings. This is a reversal of form since most World War II Soviet weapons used stampings en masse. The receiver has relatively few complex milling cuts, and an insert is used to cam the bolt into the barrel extension at the start of the locking rotation.
The AKM, 7.62x39mm
Although the original version of the AK-47 rifle had been designed around a stamped sheet metal receiver, many problems were encountered when attempting to manufacture them on a large scale. There were obvious advantages with using such a receiver including weight, material sourcing and less machining. The interim use of a forged receiver was utilized while a team of engineers worked on perfecting a suitable stamped receiver. The final prototype was successfully tested and recommended for adoption during the last months of 1958. The Avtomat Kalashnikova Modernizirovanniy, or modernized AK rifle, that would be best known as the AKM was standardized during 1959.
The AKM-stamped receiver was fabricated from a flat piece of sheet metal approximately 1mm (0.04 inch) thick; to form a receiver the metal was bent into a U shape. Like the first generation stamped receiver AK-47, the AKM receiver was designed around a machined steel trunnion block. Six rivets were used to secure the barrel trunnion in place. The guide rails for the bolt carrier to ride on were secured to the inside of the receiver walls with a series of spot welds. The cartridge case ejector was designed as part of the left guide rail, as opposed to being an integral part of the receiver itself, as on all milled receiver variants. To ensure long-term serviceability, the entire receiver was heat-treated. There were two different receiver designs: one for the fixed stock rifle and another for the folding stock model.
To add strength and rigidity to the thin receiver, a reinforcing rivet and sleeve were placed mid-way in the receiver, above the magazine release while the full-automatic trip lever was redesigned to clear the rivet. The steel backplate trunnion was secured with rivets (varies by model and country) with the rear-most rivets extending completely through both sides of the receiver adding rigidity to the receiver and as an attachment point for the buttstock. The AKM method of attaching the buttstock changed from the three-screw, two-tang arrangement of milled receiver AKs, to a simpler single top tang with two screws. The nose of the AKM buttstocks was stepped and longer in length than those used with the milled receiver to extend further inside the receiver. This added lateral strength, but the buttstocks are not interchangeable between the milled receiver and stamped receiver rifles. The backplate also had a dovetail-style channel cast or machined into the top to house the recoil spring guide, which contained the recoil spring and provided a means to secure the receiver top cover in place. Indentations, or dimples, on each side of the receiver above the magazine well serve as surfaces to hold the magazine in position, but their primary purpose is to add strength and rigidity to the sheet metal receiver. The concave shape of the magazine dimple, was an ingenious engineering solution designed to absorb and distribute some of the shock that transfers to the receiver from a fired round, as well as make the receiver more resistant to external impact forces that could otherwise distort or twist it. In the event of an out-of-battery discharge, the dimple was designed to divert and re-direct most of the shock waves. The dimple’s reinforcing and the force-redistributing effect will prevent the receiver from bulging outwards.
Steel axis pins are used for the hammer, trigger and trip sear. The holes on the left side of the receiver had elongated indentations or “dimples” around them, primarily to maintain the same inside dimensions as milled receiver models, therefore maintaining the same axis pin and fire control group dimensions. One of the more interesting innovations was the implementation of a hammer delay device that mounted on the right side of the trigger. The device consisted of a steel base with a rotating pawl and spring. When the trigger is pulled, the pawl momentarily blocks the path of the hammer, delaying its travel for a millisecond. The purpose of the device was to allow additional time for the bolt to lock into battery. Bolt-bounce was eliminated, resulting in an increase of the weapon’s accuracy. Without the hammer-retarder, the AKM did not meet the same accuracy requirements as set by the earlier milled receiver AK. The device also lowered the full-automatic cyclic rate by approximately 50 rounds per minute, earning it the incorrect nomenclature of “rate reducer.” The hammer was redesigned to accommodate the device, and the trigger was redesigned, having only one hook to engage the hammer. The new sheet metal receiver reduced the overall weight of the AKM rifle by nearly 2.5 pounds over the forged receiver Type 3 AK. Along with the new receiver, engineers had worked to resolve a few other issues that had been encountered with the original AK design. The accuracy of the AKM was thought to be increased, resulting in the rear sight being recalibrated from 800 meters to an even more optimistic 1000-meter range. The top cover is pressed from thinner sheet metal to save weight and has reinforcing ribs pressed into it in order to make it as durable as the earlier covers. The AKM gas tube does not have any gas vent holes in it; the gas vent holes were relocated to the barrel-mounted gas block. The purpose of relocating the gas system vents from the gas tube to the gas block on the AKM was to prevent dirt or sand from entering the weapon through the vent holes, which was sometimes an issue with the gas tubes of the milled rifles. Since the forward end of the gas piston normally blocks the vent holes in the gas block when the bolt carrier is in a forward position, it helps keep dirt or sand from entering the gas system through the holes; when the weapon is fired, any debris in the holes will be blown away by the gas pressure from the fired round. To reduce corrosion, the inside surfaces of the gas blocks were chromium-plated. To assist in the control of automatic fire, a simple compensator was first introduced around 1965. Fitted to the muzzle, the device is angled and canted slightly to the right. The compensator is designed to divert escaping gas from a fired round, assisting the operator in keeping the barrel from climbing upward and to the right. This design also diverts muzzle gases away from the ground and helps to minimize the dust or sand disturbed by the weapon’s muzzle blast, which could reveal the shooter’s position. A new style of bayonet was also introduced for issue with the AKM. During 1965, a new magazine made of fiber-reinforced phenol plastic was introduced. Oddly, the magazines were orange in color, which made them visibly stand out in the field. The locking lugs and feed lips of the magazine were made of steel molded into the plastic. The spring, follower, floor plates and floor plate retainers were also made of steel.
With a loaded steel 30-round magazine, the fixed stock AKM weighs 8.7 pounds (3.95kg). The overall length is 34.64 inches (880mm).
A short time after the AKM was adopted, a rail was designed to mount a variety of optical devices on the rifle.
Observations
Most transferable original select-fire AKs were brought back from Vietnam and amnesty registered in 1968. Most were Chinese-made Type 56 assault rifles, a copy of the Type 3 Soviet AK.
Importation of Egyptian and Chinese semi-automatic, stamped receiver AK rifles began during the early 1980s. A small number were legally converted to select-fire in the relatively short window before the ban in May 1986.
Some of the early 7.62mm ammunition imported from China was corrosive. Most 7.62x39mm ammo available today is made for the commercial market and non-corrosive. However, there have been several lots discovered that were found to be corrosive despite being marked and sold as non-corrosive.
RECOMMENDED READING
AK-47: The Grim Reaper II
Chipotle Publishing, LLC.
bit.ly/2pwUVD3
References
Aberdeen Proving Ground, 11th Intelligence Bn, “Technical Intelligence Bulletin TIB 0-61: The AK-47 Assault Rifle.”
Department of the Army, AK-47 Assault Rifle, 203rd Military Intelligence Battalion, Aberdeen Proving Center, Aberdeen, MD.
Ezell, Edward C., “East German Kalashnikov Rifles, Small Arms World Report,” The Institute for Research on Small Arms in International Security, 1847 Vernon Street, NW, Washington, DC, Feb. 1992.
Ezell, Edward C., “New Versions of the Kalashnikov Assault Rifle,” International Defense Review, Feb. 1981.
Rocha, John G., “Technical Notes Soviet AK-47 Rifle, U.S. Army Weapons Command Research & Engineering Directorate,” Small Arms Laboratory, 1968.
U.S. Army Foreign Science and Technology Center, Technical Translation, “The 7.62mm Kalashnikov Rifle,” 1978.
U.S. Army Foreign Science and Technology Center, “This is Kalashnikov Country: East Germany.”
U.S. Army Foreign Science and Technology Center, “The 7.62 AKM Carbine (Polish),” Aug. 15, 1968.
U.S. Army Foreign Science and Technology Center, “Warsaw Pact Bayonet-Wirecutter for the AKM Assault Rifle. FSTC-CW-07-5-68.” May 1968.
VISR Magazine Special Kalashnikov Issue, Das Internationale Waffen Magazin, Redaktionsanschrift, Wipsch 1, 56130 Bad Ems, Germany, 2002.
Smithsonian Institution Archives, 1989-1990, Kalashnikov, Collection Division 2, Video Session’s 7, 8, 9, 10, 11, 12 and 13.
The term “AK-47” has become a generic identifier for a certain class of assault rifle. The term is generally used to describe a particular Soviet-designed firearm.
This article first appeared in Small Arms Review V22N6 (June 2018) |
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