The question of the initial velocity of a bullet fired from a modernized Kalashnikov assault rifle (AKM) is fundamental to understanding the ballistic capabilities of this legendary model of small arms. The standard value accepted in reference literature and military manuals is considered to be an indicator in 715 meters per second. However, this figure is not an absolute constant and depends on many factors, including powder temperature, barrel length and bullet weight.
Exactly initial speed determines the flatness of the trajectory, penetrating ability and energy of the bullet at various distances. For engineers and ballisticians, this is a key parameter that allows them to calculate the effective firing range. In the case of a cartridge 7.62×39 mm, which is the main one for the AKM, the combination of moderate speed and heavy bullet creates a unique lethality profile, different from Western counterparts of the time.
In this article we will analyze in detail what the actual projectile departure speed depends on, how it changed during the modernization process from AK-47 to AKM, and what practical conclusions can be drawn from these figures. Understanding these processes is necessary for an objective assessment of the combat qualities of weapons.
Evolution of speed: from AK-47 to AKM
The transition from the first model of the Kalashnikov assault rifle (AK-47) to the modernized version (AKM) brought not only changes in production technology, but also influenced the ballistic characteristics. Although the cartridge remained the same - 7.62×39 mm M43, changes in the design of the barrel and powder charge made it possible to optimize the parameters of the shot. If earlier versions could show a dispersion of speeds due to less advanced barrel manufacturing technology, then the AKM became the standard of stability.
The key difference was the introduction of higher quality steel and improved bore processing. This made it possible to reduce the resistance to bullet movement and minimize the energy loss of powder gases. The initial speed of 715 m/s was achieved precisely thanks to the debugging of the technological process and the use of more stable powder compositions, which ensured high accuracy of combat at medium distances.
⚠️ Attention: The initial speed of an AKM bullet should not be confused with the speed of a rifle cartridge bullet (for example, 7.62x54 mm R), which is much higher and can reach 800-850 m/s. The intermediate power cartridge has its physical limitations.
It is important to note that the stability of the initial speed directly affected the survivability of the barrel. For the AKM, this parameter was improved, which made it possible to maintain the declared ballistic characteristics throughout the entire service life of the weapon. The engineers achieved a balance between shot power and ergonomics, which made the machine gun a universal tool.
Factors affecting bullet speed
The figure of 715 m/s indicated in the performance characteristics is average and measured under ideal conditions. In reality, the velocity of a bullet is affected by a number of variables that must be taken into account when making ballistic calculations. Ambient temperature plays a critical role: cold powder burns more slowly, reducing barrel pressure and, as a result, muzzle velocity.
Barrel length is the second most important factor. The standard AKM barrel has a length of 415 mm (calibers). Any change in this length, for example by using shorter versions or, conversely, longer barrels, will result in a change in speed. The condition of the cartridge also affects: the humidity of the gunpowder or the substandard cartridge case can significantly change the internal ballistics of the shot.
- 🌡️ Air temperature: At low temperatures, the speed can drop by 10-20 m/s, which affects the point of impact.
- 📏 Barrel length: Shortening the barrel by 100 mm can reduce the speed by about 30-40 m/s.
- 💊 Gunpowder batch: Different batches of gunpowder have different burning rates, which creates a spread in initial velocities.
In addition, wear of the bore (carbon deposits, erosion of rifling) leads over time to a decrease in the compression of powder gases. This means that an old, intensively fired machine gun will have an initial bullet speed lower than the rated speed. Regular cleaning and maintenance of the weapon is required to maintain performance.
When storing ammunition in high humidity conditions, bullet velocity may decrease due to changes in the chemical properties of the powder, so store ammunition in an airtight container.
Comparison table of characteristics
For a more visual presentation of the data, it is advisable to consider a comparative table showing the difference between the basic AK-47 and the modernized AKM. Despite the similarity in caliber, technological improvements have made adjustments to the final figures.
| Parameter | AK-47 (early) | AKM (modernized) | Unit of measurement |
|---|---|---|---|
| Initial bullet speed | ~700 | 715 | m/s |
| Barrel length | 415 | 415 | mm |
| Muzzle energy | ~1950 | ~2030 | J |
| Bullet weight | 7.9 | 7.9 | g |
As can be seen from the table, the speed increase is small, but it is ensured by a more stable production process. Muzzle energy also increased, which had a positive effect on penetration ability at distances up to 300 meters. The bullet weight remained unchanged, since the ballistic coefficient of the cartridge 7.62×39 has already been optimized.
⚠️ Attention: The use of cartridges with enhanced penetration (IP) bullets may slightly change the muzzle velocity due to differences in core weight and shape, despite the same caliber.
Ballistic properties of a 7.62 mm bullet
Cartridge bullet 7.62×39 mm has a unique combination of weight and speed. With a mass of about 7.9 grams and a speed of 715 m/s, it has significant momentum. This provides good stopping power when hitting a target, but at distances over 400 meters the bullet begins to quickly lose energy due to the high aerodynamic drag coefficient.
The flight trajectory of the AKM bullet is quite flat at distances of up to 300 meters, which allows for effective shooting without complex adjustments. However, after passing the sound barrier and reducing speed below 300 m/s, the bullet becomes susceptible to crosswinds. Ballistic coefficient This bullet is inferior to modern low-pulse cartridges, but superior to many pistol calibers.
The rotation of the bullet, imparted by the rifling of the barrel (rifling pitch 240 mm), stabilizes it in flight. The rotation speed at the barrel exit is tens of thousands of revolutions per minute. This rotation is critical to accuracy: if the bullet were fired at a slower speed or the barrel was worn out, accuracy would drop to unacceptable levels.
Effect of bullet shape on range
The 7.62×39 cartridge has a blunt nose compared to rifle bullets, which creates air turbulence and reduces velocity faster. That is why the effective range is limited to 400-500 meters, despite the high initial energy.
Practical application and effective range
Knowing the initial speed, you can determine the effective firing range. For a single fire it is up to 500 meters, and for automatic fire - up to 300 meters. At long distances, the bullet loses not only speed, but also accuracy, as well as sufficient energy to ensure a guaranteed hit to a protected target.
In urban conditions or in the forest, where distances rarely exceed 200 meters, an initial speed of 715 m/s is excessive and even optimal. It provides a flat trajectory, making aiming easier. However, in open spaces the fighter must take into account the reduction in speed and a significant reduction in trajectory.
- 🎯 Distance 100 m: The bullet covers the distance in 0.14 seconds, the reduction is minimal.
- 🎯 Distance 300 m: Flight time is about 0.45 seconds, corrections for descent are required.
- 🎯 Distance 500 m: The speed drops to 250-280 m/s, the energy becomes borderline for breaking through modern body armor.
Thus, the tactics for using AKM are based precisely on taking advantage of the initial speed at short and medium distances. Attempts to snip at extreme ranges with this weapon are ineffective due to the rapid loss of kinetic energy.
☑️ Checking ballistic conditions
Myths and reality about AKM speed
There are many myths surrounding the technical characteristics of the AKM. One of them says that the AKM bullet flies slower than sound only at short distances. In reality, the bullet remains supersonic (sound speed ~330 m/s) up to a distance of about 600 meters, after which it goes into subsonic flight mode.
Another common myth concerns the "ricocheting" bullet. The high initial speed actually promotes ricocheting off hard surfaces (rocks, concrete, water) at sharp angles. However, this property is inherent in any projectile with high kinetic energy, and not just the 7.62 mm cartridge. Kinetic energy in joules at the barrel cut is more than 2000 J, which is comparable to the energy of a passenger car moving at a speed of 60 km/h.
⚠️ Attention: When shooting at solid obstacles, there is a high risk of AKM bullet ricochet, which can be dangerous for the shooter and others. Always control the direction of the shot and the background behind the target.
The reality is that the AKM is a close-to-medium combat weapon, where its speed characteristics are revealed as fully as possible. Attempts to attribute to it the properties of a long-range rifle or, conversely, to compare it with a submachine gun are erroneous.
The initial speed of 715 m/s is the optimal balance between penetration, recoil and weight of wearable ammunition for an infantryman.
Why is the initial speed of the AKM lower than that of the SKS rifle?
Although the AKM and SKS have the same cartridge (7.62×39), the SKS has a longer barrel length (520 mm versus 415 mm for the AKM). A longer barrel allows the powder gases to act on the bullet longer, accelerating it to 730-740 m/s. However, increasing the length of the barrel reduces the maneuverability of the machine gun in combat.
Does bullet type (steel or lead core) affect velocity?
The mass of the bullet remains almost the same (about 7.9 g), so the initial velocity changes slightly. The difference can be several meters per second due to minimal differences in diameter or shape, but in practical shooting the difference is not noticeable.
Is it possible to increase the speed of an AKM bullet?
Theoretically, it is possible by using more powerful gunpowder or lengthening the barrel. However, this will require reworking the weapon and may lead to rapid wear or destruction. The standard 7.62x39 cartridge is already at the pressure limit that is safe for this design.