The AK-74 was designed by А. D. Kryakushin's group under the design supervision of Mikhail Kalashnikov. It is an adaptation of the
7.62×39mm AKM assault rifle and features several important design improvements. These improvements were primarily the result of converting the rifle to the intermediate-calibre high velocity
5.45×39mm cartridge. In fact, some early models are reported to have been converted AKMs, re-barreled to 5.45×39mm. Compared with the preceding AKM, the AK-74 has better effective firing range, accuracy (a main development goal), and reliability. About 50% of the parts in the AK-74 and AKM are the same (including pins, springs and screws).
Operating mechanism The rifle's operation during firing and reloading is identical to that of the AKM. After ignition of the cartridge primer and propellant, rapidly expanding propellant gases are diverted into the gas cylinder above the barrel through a vent near the muzzle. The build-up of gases inside the gas cylinder drives the long-stroke piston and bolt carrier rearward and a cam guide machined into the underside of the bolt carrier along with an ejector spur on the bolt carrier rail guide, rotates the bolt approximately 35° and unlocks it from the barrel extension via a camming pin on the bolt. The moving assembly has about of free travel which creates a delay between the initial recoil impulse of the piston and the bolt unlocking sequence, allowing gas pressures to drop to a safe level before the seal between the chamber and the bolt is broken. Like previous Kalashnikov-pattern rifles, the AK-74 does not have a gas valve; excess gases are ventilated through a series of radial ports in the gas cylinder. Since the Kalashnikov operating system offers no
primary extraction upon bolt rotation, the 5.45×39mm AK-74 bolt has a larger extractor claw than the 7.62×39mm AKM for increased extraction reliability. Other minor modifications were made to the bolt and carrier assembly.
Barrel The rifle received a new barrel with a
chrome-lined bore and 4 right-hand grooves at a 200 mm (1:7.87 in) or 37 calibers
rifling twist rate. The front sight base and gas block were redesigned. The gas block contains a gas channel that is installed at a 90° angle in relation to the bore axis to reduce bullet shear at the port hole. A pair of support brackets are cast into the gas block assembly and are used to attach a BG-15c or
GP-25 underslung 40 mm grenade launcher. Like the AK-47 and AKM, the muzzle is threaded for the installation of various muzzle devices such as the standard
muzzle brake or a
blank-firing adaptor, while a spring-loaded detent pin held in the front sight post prevents them from unscrewing while firing. However the muzzle threads have been relocated to the front sight base for both easier and more economic replacement in case of thread damage. The distinctive standard-issue muzzle brake features a large expansion chamber, two symmetrical vertical cuts at the forward end of the brake and three non symmetrical positioned vent holes to counteract
muzzle rise and climb as well as lateral shift to the right much like the AKM's offset muzzle brake. A flat plate near the end of the brake produces a forward thrust when emerging exhaust gases strike its surface, greatly reducing recoil. The muzzle brake prevents backblast from reaching the firer, although it is reported to be harsh on bystanders as the muzzle gases are dispersed to the sides. The standard-issue AK-74 muzzle brake has been subtly revised several times since the 1970s.
Sights Iron sights The AK-74 uses an adjustable notched rear tangent
iron sight calibrated in increments from . The front sight is a post adjustable for elevation in the field. Horizontal adjustment requires a special drift tool and is done by the armoury before issue or if the need arises by an armourer after issue. The sight line elements are approximately over the bore axis. The "
point-blank range" battle zero setting "
П" standing for
постоянная (constant/consistent/permanent) the 5.45×39mm AK-74 rear tangent sight element corresponds to a zero, compared with the zero for 7.62×39mm AKs. For the AK-74 combined with the 7N6 or 7N10 service cartridges the 400 m battle zero setting point-blank range limits the
apparent "bullet rise" within approximately under the line of sight. At the corresponding maximum point-blank range the bullet will have dropped to approximately relative to the line of sight. Soldiers are instructed to fire at any target within this range by simply placing the sights on the center of mass (the belt buckle, according to Russian and former Soviet doctrine) of the enemy target. Any errors in range estimation are tactically irrelevant, as a well-aimed shot will hit the torso of the enemy soldier. For the 5.45×39mm AK-74, the East German
Zeiss ZFK 4×25,
USP-1 (1P29), Belorussian
BelOMO PO 3.5×21P,
PO 4×24P and the
1P78 Kashtan dedicated side rail mounted optical sights were developed. These optical sights are primarily designed for rapid target acquisition and first round hits out to 400 m, but by various means these optical sights also offer
bullet drop compensation (BDC) (sometimes referred to as
ballistic elevation) for aiming at more distant targets. The BDC feature compensates for the effect of
gravity on the
bullet at given distances (referred to as "
bullet drop") in flat fire scenarios. The feature must be tuned for the particular ballistic trajectory of a particular combination of gun and
cartridge at a predefined
muzzle velocity and
air density. Since the usage of standardized ammunition is an important prerequisite to match the BDC feature to the
external ballistic behaviour of the employed projectiles, these military optical sights are intended to assist with field shooting at varying medium to longer ranges rather than precise long range shots. The standard Russian side rail mounted optical sight was the 4×26
1P29 Universal sight for small arms. It was copied from and hence similar to the British
SUIT (Sight Unit Infantry, Trilux). When mounted the 1P29 sight is positioned centered above the receiver at a height that allows the use of the iron sights. It weighs 0.8 kg, offers 4× magnification with a field of view of 8° and 35 mm eye relief. The 1P29 is issued with a canvas pouch, a lens cleaning cloth, combination tool, two rubber eyecups, two eyecup clamps and three different bullet drop compensation (BDC) cams for the AK-74/
AN-94,
RPK-74 and
PK machine gun. The 1P29 is intended for quickly engaging point and area targets at various ranges and is zeroed for both windage and elevation at . On the right side of the field of view a
stadiametric rangefinder is incorporated that can be used to determine the distance from a tall object from . The
reticle is an inverted aiming post in the top half of the field of view and is
tritium-illuminated for low-light condition aiming. The current Russian standard side rail mounted optical sight for the AK-74M is the 2.8×17
1P78 Kashtan, an aiming optic similar to the American
ACOG. When mounted the 1P78 sight is positioned centered above the receiver. It weighs 0.5 kg, offers 2.8× magnification with a field of view of 13° and 32 mm eye relief. The 1P78 comes in several versions for the AK-74 (1P78-1),
RPK-74 (1P78-2),
AKM (1P78) and
RPK (1P78-3). The 1P78 is intended for quickly engaging point and area targets at various ranges and is zeroed for both windage and elevation at . A
stadiametric rangefinder is incorporated that can be used to determine the distance for a soldier sized target from . The
reticle consist of a main 400 m "chevron" (^), a holdover dot and smaller additional holdover chevrons for and and is
tritium-illuminated for low-light condition aiming.
New features on exercise with the AKS-74 variant featuring plum-colored polymer furniture The AK-74 was equipped with a new buttstock, handguard (which retained the
AKM-type finger swells) and gas cylinder. The stock has a shoulder pad different from that on the AKM, which is rubber and serrated for improved seating against the shooter. In addition, there are lightening cuts on each side of the buttstock. The buttstock, lower handguard and upper heatguard were first manufactured from
laminated wood, this later changed to a synthetic
fiberglass-reinforced
polyamide 6 colored with "kaprozol brown 4K" disperse dye, the color of which is usually referred to as "Russian
Plum". The introduction of the new material was slow and impeded by very stringent hardness requirements of the military which no Western polymer furniture was able to satisfy as of 1980. The AK-74 gas tube has a spring washer attached to its rear end designed to retain the gas tube more securely. The lower handguard is fitted with a leaf spring that reduces play in the rifle's lateral axis by keeping the wood tensioned between the receiver and the handguard retainer. The receiver remains nearly identical to that of the AKM; it is a U-shaped thick
sheet steel pressing supported extensively by pins and rivets. The internal guide rails on which the bolt carrier travels are
stamped and
spot welded to the inside of the receiver housing. Minor changes were made to the front barrel and rear stock trunnions as well as the magazine well. All external metal surfaces are coated with a glossy black enamel paint.
5.45×39mm cartridge Relatively small sized, light weight, high velocity military service cartridges like the 5.45×39mm allow a soldier to carry more ammunition for the same weight compared with their larger and heavier predecessor cartridges, have favourable maximum
point-blank range or "battle zero" characteristics and produce relatively low
bolt thrust and
free recoil impulse, favouring light weight arms design and automatic fire accuracy. Tests measured the free recoil energy delivered by the 5.45×39mm AK-74 rifle at , compared with delivered by the 7.62×39mm in the AKM. Early 5.45×39mm ballistics tests demonstrated a pronounced tumbling effect with high speed cameras. Some Western authorities believed this bullet was designed to tumble in flesh to increase wounding potential. At the time, it was believed that
yawing and
cavitation of projectiles were primarily responsible for tissue damage.
Martin Fackler conducted a study with an AK-74 assault rifle using live pigs and
ballistic gelatin; "The result of our preset test indicate that the AK-74 bullet acts in the manner expected of a full-metal-cased military ammunition – it does not deform or fragment when striking soft tissues". Most organs and tissue were too flexible to be severely damaged by the temporary cavity effect caused by yaw and cavitation of a projectile. With the 5.45 mm bullet, tumbling produced a temporary cavity twice, at depths of and . This is similar to (but more rapid than) modern 7.62×39mm ammunition and to (non-fragmenting)
5.56×45mm NATO ammunition.
Magazines The original steel-reinforced 30-round AK-74 detachable box magazine was similar to that of the AKM, except for minor dimensional changes required by the 5.45×39mm cartridge. These magazines discolour over time from yellowish to
rust-coloured shades, and are often mistakenly identified as being made of
Bakelite (a
phenolic resin), but were actually fabricated from two-parts of AG-4S molding compound (a
glass-reinforced phenol-formaldehyde binder impregnated composite), assembled using an
epoxy resin adhesive. Noted for their durability, these magazines did however compromise the rifle's camouflage and lacked the small horizontal reinforcing ribs running down both sides of the magazine body near the front that were added on all later AK-74 magazine generations. is also interchangeable with that of the AK-74. The empty weight of a 45-round RPK-74 box magazine is . Further 60-round and later 50-round quad-stack 5.45×39mm
casket magazines were developed. The transition to mainly plastic magazines and the relatively small sized, light weight, high velocity 5.45×39mm cartridge yielded a significant weight reduction and allows a soldier to carry considerably more rounds for the same weight compared with the previous Soviet AK-47 and AKM and later 7.62×39mm chambered AK platform assault rifles. The blade has a new spear point and an improved one-piece molded plastic grip making it a more effective fighting knife. It also has saw-teeth on the false edge and the usual hole for use as a wire-cutter. ==Variants==