BBM ASLAV 8x8 Australian Army with M242 BUSHMASTER gun
Requirements and technologies
Medium-caliber automatic guns, intended for installation on armored combat vehicles (BBM), have been constantly developed over the past decades. This applies to their characteristics and operating principles, as well as relevant operational concepts.
In this article, we briefly note the key factors of the growing demand for weapons of this class and the impact of these needs on the choice of the optimal caliber and other characteristics, and then proceed to the description of the defining technologies of modern models.
Large gauges for growing needs
First attempts to arm BBM with more powerful automatic weapons compared to the ubiquitous heavy machine guns (M2 12,7 mm in the West and KPV 14,5 mm in the Warsaw Pact countries) began at the end of 50 and the beginning of 60 in the framework of the general “motorization” of infantry units that affected all the leading armies of the world.
In the West, initially these works, as a rule, consisted in the refinement of automatic guns, originally designed for installation on combat aircraft or anti-aircraft installations. The first tower systems of this type included mainly the Hispano Suiza HS-820 cannon (with a camera for the 20x139 projectile), which was installed on German SPZ 12-3 machines (1800 machines were made for the Bundeswehr in 1958 - 1962 years) and reconnaissance version M-114, and reconnaissance version M-113, and the reconnaissance version M-X-NNXX. tracked armored personnel carrier M-1 US Army. On the other hand, the Russians initially adopted a unique approach, equipping their new BMP-73 (the predecessor of all infantry combat vehicles) 2A28 XNUMX-mm low-pressure thunder cannon, without dividing the Western choice in favor of medium-sized automatic guns. However, they appeared on their next generation machines.
However, these first applications of automatic guns on armored fighting vehicles immediately confirmed not only the very important operational need for them, but also revealed the corresponding shortcomings of the weapons used at that time. Unlike aviation and anti-aircraft weapons, automatic anti-aircraft guns are used to attack a wide range of targets, from unarmored to fortified and armored, often in the same battle. Accordingly, the presence of a dual feed system, which would allow the shooter to quickly switch from one type of ammunition to another, became mandatory.
HS-820 was a cannon with a single supply path, and remained so even after refinement and the receipt of a new designation Oerlikon KAD. For this reason, as well as for industrial policy reasons, at the beginning of 70-s, Rheinmetall and GIAT developed and introduced a new generation of dual-feed 20-mm guns: Mk20 Rh202 for MARDER and M693 F.1 for AMX-10P, respectively.
The progressive increase in requirements for armor penetration of guns BMP as a result of the emergence of enemy vehicles with enhanced protection
Oerlikon KBA cannon (currently Rheinmetall DeTec) with a cam for 25x137 ammunition
Comparison of the size of the main types of ammunition currently used (or proposed) for automatic guns BMP. From left to right, 25x137, 30x173, 35x228, 40x365R and telescopic 40x255
CT40 gun with loading mechanism and related ammunition
Both Mk20 and M693 guns fired 20 x 139 projectiles, but immediately after they appeared doubts arose about the characteristics of these munitions, which could really satisfy the rapidly developing operational needs regarding the effective distance of the lesion, the impact of the projectile on the final trajectory and armor-piercing strength, especially then dominant concept of warfare in Central Europe. In these scenarios, providing fire support to dismounted infantry units was considered primarily from the point of view of defeating enemy light / medium BBM. Accordingly, one of the most important characteristics of fire support needed for such weapons was a large penetration capability at distances to 1000 - 1500 m. Currently, the smallest caliber capable of penetrating 25 mm thick armor with an 30 inclination (i.e. BMP-1) from 1000 meters , is 25 mm. This led to the fact that several Western armies, primarily led by the United States, missed the generation of 20-mm weapons for their BMP and switched from 12,7-mm machine guns to weapons with the powerful 25 x 137 Swiss projectile. This weapon can be considered as the first, specially designed automatic guns intended for installation on the BMP.
Armament firing 25 x 137 ammunition is currently installed on many different tracked and wheeled APCs, including the American M2 / M2 BRADLEY and LAV25, the Italian DARDO, the Danish M-113A1 with T25 tower, the KI-17THIHIHIHIXIXIXAXIXIXXXXXXXXXXXXXXXXXXXXXX-A-1, the Canadian KIHIHIHIXIXIXIXIXIXIXXXXXXXXXXXXXXXX-25 87 XNUMX XNUMX ammunition firing ammunition XNUMX x XNUMX, is currently installed on many different tracked and whelpas. Japanese Type XNUMX, Singaporean BIONIX, Kuwaiti DESERT WARRIOR and Australian ASUW.
But “the appetite comes with eating” and a couple of leading armies realized that even 25-mm weapons are not powerful enough. This was due not so much to the same great fears that led to the rapid displacement of the 20 caliber mm with the 25 caliber mm, but rather with a broader perception of the role and task of the BMP. In addition to fire support of dismounted infantry units, infantry fighting vehicles were regarded as an auxiliary combat vehicle for the OBT, responsible for hitting targets that do not require large-caliber ammunition, as well as a kind of “mini-OBT” in scenarios with a lower level of threats. In this case, a gun is needed, capable of firing not only with armor-piercing projectiles, but also high-explosive fragmentation with an appropriate explosive charge.
Accordingly, the British and the Soviet army made thus transition to 30 mm introducing gun RARDEN (x munition 30 170) for machines and WARRIOR SCIMITAR gun and 2A42 (x 30 165) for BMP-2 and BMD-2. Similarly, at the beginning of the 80, the Swedish army launched a program on its BMP (ultimately CV90) and decided to install the Bofors 40 / 70 cannon on it, firing powerful 40 x 365R ammunition.
Rheinmetall Mk30-2 / AVM was developed as the main weapon of the new German BMP PUMA
Relatively recent embodiments of this concept are unique dvuhkaliberny arming unit 2K23 from PCU mounted on the Soviet / Russian BMP-3 (automatic 30-mm gun 2A42 + 100-mm 2A70 gun), and Rheinmetall Rh 503, originally designed for the "unfortunate» MARDER 2 and having an 35 x 228 shot camera. The latter cannon has the potential for further growth, as it can go to the 50 x 330 "Supershot" telescopic projectile by simply replacing the barrel and several components. Despite the fact that the Rh 503 has never been mass-produced, the innovative concept of a quick caliber change aroused interest; It was adopted in particular for BUSHMASTER II (30 x 173 and 40 mm Supershot) projects and BUSHMASTER III (35 x 228 and 50 x 330 Supershot) projects, although none of the operators of these guns have yet taken advantage of these opportunities. .
Currently, there is a kind of general agreement in the sense that 30-mm armament is minimal, which can be installed on the latest generation of armored infantry fighting vehicles and reconnaissance vehicles. With regard to user choice, here is the Type 89 machine with the 35-mm gun, the Dutch and Danish solution for installing the 35-mm gun on your CV90, upgrading the Singapore BIONIX machine and installing the 30-mm gun (BIONIX II), the intention of British Army finally certify CT40 cannon from CTA International (BAE Systems + Nexter), shooting unique 40 x 255 telescopic shots to upgrade British WARRIOR machines (the so-called Warrior BMP Extension Program - WCSP), as well as for promising machines FRES Scout and finally Adopting a South Korean BMP K21 with the local option 40 / 70 gun.
At least, all the above-mentioned European solutions were probably motivated by the return of emphasis to armor-piercing characteristics, based on the understanding that even 30-mm armor-piercing sabot shells (APFSDS) cannot satisfactorily handle the latest Russian BMP-3 with additional booking. In a broad sense, it is important to note that the current deployment of many armies in asymmetrical combat scenarios leads to the introduction of increasingly heavy additional booking kits for infantry fighting vehicles. Despite the fact that this additional armor is mainly designed to protect against improvised explosive devices (IEDs) and RPG-type threats, rather than from automatic cannon fire, it can be assumed that advanced high-end BMPs will need at least 35 – 40 -mm weapons for the successful struggle with modern machines of the same class.
And here comes the puzzle. It is quite obvious that the armament of the BMP cannon caliber 35 - 40 mm in the tower already includes certain compromises regarding the combat weight and the size of the machine (with a direct negative impact on strategic mobility), the allowable ammunition and most importantly the number of infantrymen transported. By increasing the caliber, you can then actually create a light tank with minimal internal space for infantrymen and their regular weapons, both individual and branch armament. If increased armor-piercing capabilities should actually be perceived as mandatory, perhaps the most practical way to achieve this goal is to rely solely on ATGMs, whereas the gun could be optimized mainly, but not exclusively, to destroy unarmored or partially armored targets. Thus, we see a full cycle of return to the philosophy of the BMP-1.
As for the progress in ammunition, the two most significant events were probably the appearance of APFSDS armor-piercing shells (armor-piercing sabot with a stabilizing shank (feathered)) for 25-mm (and larger) weapons, and the development of high-explosive ordnance ABM (Air Bursting) Munition - Air Explosion Projectile) or HABM (high-speed ABM) technology with an inductive electronic fuse; first here was the concept of AHEAD from Oerlikon for shells from 30 mm and above. These projectiles allow you to effectively strike personnel, located behind natural shelters.
Apparently, a secondary, but really important issue in connection with the installation of automatic guns of BBM is the removal of spent cartridges, preventing their rebound inside the fighting compartment, so they become potentially dangerous. On the photo of the DARDO infantry fighting vehicle of the Italian army with the Oerlikon KBA 25 mm cannon, open hatches for ejection
On the Swedish BMV CV90 installed version of the ubiquitous anti-aircraft gun Bofors 40 / 70; when installed, it flips on 180 degrees
Simplified concept of a chain driven cannon
Proceeding from the firing regimes of powerful ammunition, all automatic armored vehicles for BBM, which are currently available on the market, are distinguished by tight locking, that is, the breech block is rigidly locked with the receiver / barrel assembly during firing. This can be obtained by either a butterfly valve with locking protrusions (for example, Oerlikon KBA 25 mm), shutters with retractable locking combat shutters (retractable locking flaps) (for example, Rheinmetall Mk20 Rh-202, GIAT MS93 F1) and vertical. (for example, Bofors 40 / 70) or horizontal (RARDEN) sliding gates. The revolutionary CTA 40 gun is special in its class, it is characterized by a horizontally rotating (90 degrees) charging chamber, separated from the barrel.
As for the principles of operation, most of the usual practical concepts of such weapons consist in a long rollback, work due to removal of gases, hybrid systems and power from an external source.
The appearance of 25 x 137 armor-piercing sub-caliber ammunition significantly improved the armor-piercing characteristics of 25-mm weapons
Prototype BMP WARRIOR with the CT40 gun installed during firing tests
In all armaments that use recoil forces and rigid locking, the energy required to perform the firing cycle is applied to the bolt due to the reverse movement of the bolt itself and the barrel, locked together and rolled away under the pressure of powder gases. In the system with a “long recoil”, the bolt and barrel roll back a distance greater than the length of the non-shot projectile. When the pressure in the chamber decreases to acceptable levels, the shutter is unlocked and begins the opening / removing sequence of the liner, while the barrel returns to the front position, the shutter then also moves forward due to its spring, sends a new shot and locks it.
This principle offers a certain set of advantages for tower armament designed to destroy ground targets. The movement back, being relatively less intensive than in the case of the short-roll design, is transformed into smaller forces transmitted to the mechanisms of the gun and its installation, which improves the accuracy of firing. In addition, the shutter, locked for a longer period of time, facilitates the removal of powder gases through the muzzle and prevents them from getting into the fighting compartment of the machine. These advantages have to pay a relatively low rate of fire, but this is not a significant problem for the BMP.
A typical example of weapons based on the work of a long recoil is RARDEN 30 mm and Bofors 40 / 70. It is also interesting to note that two manufacturers that are traditional supporters of gas-fired designs, namely the Swiss company Oerlikon (now Rheinmetall DeTec) and the Russian company KBP, adopted the concept of a long recoil for weapons specially designed for installation on BMP (KDE 35 mm for Japanese Type 89 and 2A42 30 mm for BMP-3, respectively).
The principle of operation due to the removal of gases
Originally developed by John Browning, this system relies on energy derived from the pressure of powder gases discharged at some point along the barrel. While several variants of this concept are used in handguns, most of the automatic guns operating with exhaust gases for infantry fighting vehicles are based either on the piston principle, where gases press on the piston, which is directly connected to the bolt and pushes it back, or on the principle gas exhaust when gases transfer energy directly to the slide frame.
When compared with the principle of direct recoil, the advantage of the principle of action due to the removal of gases is that the barrel is fixed (and, therefore, accuracy is increased), it is possible to adjust the firing cycle in accordance with weather conditions and the type of ammunition due to the appropriate setting of the gas release valve . On the other hand, the entire gas system must be carefully fitted to prevent toxic powder gases from entering the crew compartment.
In many designs of automatic guns, gas work is actually associated with other concepts, leading to what might possibly be called a hybrid (mixed) process (although this is not a universally accepted definition).
The most common solutions combine gas operation with recoil (thus, the energy required to carry out the firing cycle affects the valve due to the reverse movement of the liner caused by the pressure of the gas). The gases emitted from the barrel are used only to unlock the bolt from the receiver, after which the back gases push the bolt back. The whole implement is then rolled back to 20 - 25 mm, this energy is used to operate the feed system.
Such a principle “gas operation + free gate” allows using relatively easy and simple mechanisms, which led to the adoption of this principle for Hispano Suiza automatic guns after the Second World War (for example, HS-804 20 x 110 and HS-820 20 x 139), as well as for several guns from Oerlikon, GIAT and Rheinmetall.
The operation of gases can also be combined with recoil of the barrel, as is customary, for example, for the Oerlikon KBA cannon (25 x 137), originally developed by Eugene Stoner.
The Danish (in the photo) and the Dutch army chose the ATK BUSHMASTER III cannon, firing powerful 35 x 228 ammunition. It is also possible to upgrade to a version of the 50 x 330 "Supershot" for installation on the new BMP CV9035
The twin gun Nexter M693 F1 on tank AMX-30. It has a piston mechanism with exhaust gas and a rotary shutter with retractable locking shutters
The Rheinmetall Rh 503 cannon pioneered the concept of an automatic cannon, which is capable of firing ammunition of two different calibers by simply replacing the barrel and several components.
Armament with external power supply
The most typical examples of externally powered automatic cannons are probably Gatling's revolving designs and designs, but they are definitely designed to achieve high rate of fire and thus are not interesting for installation on BBM. Rather, external-powered armament mounted on an armored vehicle is mainly intended to enable the rate of fire to be adapted to the particular characteristics of the targets being hit (the rate of fire, however, is always less than that of similar weapons acting by venting). This type can be easier, cheaper and requires less volume. In addition, an external powered armament is by definition free from misfires, due to the fact that a defective shot can be extracted without interrupting the firing cycle.
Critics of the concept of weapons with external power pay attention to the fact that any damage and damage to the electric motor and / or power supply can make the gun inoperative. While this is certainly true, at the same time, it should be borne in mind that turning off the power will also damage optical-electronic devices (scopes, displays and a stabilization system), and in this case the armament working due to recoil, it actually becomes useless.
The Chain Gun chain gun (a registered trademark, not a general definition) developed at the beginning of 70 by the then Hughes company (later McDonnell Douglas Helicopters, later Boeing, now ATK) uses an electric motor to drive a chain that moves along a rectangular contour through 4 asterisks. One of the chain links is connected to the bolt and moves it back and forth for loading, firing and removing and ejecting the sleeves. During each complete cycle consisting of four periods, two periods (movement along the long sides of the rectangle) determine the time required for moving the bolt forward and loading the projectile into the chamber and extracting it. The remaining two periods during the movement of the chain on the short sides of the rectangle determine how long the shutter remains locked during firing and open to extract the liner and ventilate the powder gases.
Since the time it takes for the chain to complete a full cycle in a rectangle determines the rate of fire, a change in engine speed allows the chain gun to fire, in principle, with a continuous speed varying from single shots to the maximum safe rate of fire depending on the speed of pressure drop in the barrel after the shot, mechanical endurance and other factors. Another important advantage is that the design allows you to have a very short receiver, which facilitates the installation of weapons inside the tower.
The most famous and widely spread chain guns are the BUSHMASTER cannons, including the M242 (25 x 137), Mk44 BUSHMASTER II (30 x 173) and BUSHMASTER III (35 x 228).
Nexter Electrical System
The Nexter M811 25 x 137 cannon is mainly installed on the new VBCI 8x8 infantry fighting vehicle, and is also in service with the Turkish army (ACV); It is based on the patented external drive concept. The electric motor drives the cam shaft inside the receiver, whose rotation locks and opens the bolt, as it moves back and forth. This roller is also connected by gear to the feed mechanism so that the loading is precisely synchronized with the movement of the shutter. Shooting modes - single shot, short burst and continuous burst.
The so-called Push Through system developed by CTA International for its armament CT 40 uses the most innovative, if not revolutionary, principle of operation among all described in this article. In this case, there is a very strong link between the principle of operation and the ammunition, consisting in the fact that the concept of "pushing through" strictly depends on the availability of telescopic ammunition with a perfect cylindrical shape.
Cylindrical ammunition allows you to use the loading mechanism, in which the powder chamber is not part of the barrel, but rather a separate unit that rotates around the axis on the 90 ° electric motor for loading. Each new projectile pushes the previous cartridge case (hence the “pushing”), after which the camera turns to align with the barrel for firing. This completely eliminates the entire extraction / removal sequence required for conventional “bottle” ammunition, leading to a simpler and more compact mechanism and loading process with smaller moving parts, which would ideally be suitable for installation inside the tower. The CT cannon occupies about the same space as a regular 25-mm gun, but at the same time, it offers much higher performance (for example, the APFSDS armor-piercing projectile will pierce steel armor with a thickness more than 140 mm). Also, this unique loader mechanism allows the breech to be removed far in advance, thereby the communication between crew members and its “fighting qualities” are significantly improved.
However, it should be noted that this elegant and (apparently) simple principle of operation really requires a thoroughly crafted design and high production culture in order to guarantee a general gas-tightness between the powder chamber and the barrel.
Schematic representation of the principle of operation of the CT40 gun with telescopic ammunition
APFSDS 35 x 228 projectile (left) and corresponding 50 x 330 "Supershot" ammunition (center and left)
The Rheinmetall RMK30 (pictured during shooting tests on the WIESEL conveyor belt) is the world's first recoilless automatic gun. It has an external drive, a three-chamber turret design, shoots 30 x 250 bezgolzovye ammunition, while part of the powder gases is thrown back, compensating for rollback; This allows for lighter and less durable structures. Although RMK30 was originally designed for installation in helicopters, it can also be used in combat modules on light BBM
The ABM (air burst munition) ABM split air munition model with a programmable fuse. The projectile has an electronic module that is programmed inductively at the muzzle (by compensating for different initial speeds) in order to guarantee accurate delivery of the warhead. ABM ammunition is capable of striking a wide range of targets on a modern battlefield, including infantry fighting vehicles, ATGM installations, dismounted troops and helicopters.
ATK's BUSHMASTER II cannon is designed for 30 x 173 ammunition, but can easily be remade to fit Supershot 40-mm shots
While all the principles of work described above are currently used simultaneously and in parallel, there is an unmistakable trend in the West in the direction of accepting structures with external power, while the Russians remain loyal to the traditional concepts of gas offtake. With regard to the choice of caliber, here, in addition to operational considerations, industrial and financial issues also play an important role. In particular, the typical example is the Bundeswehr. The German army initially adopted 20 x 139, at the beginning of 80-s deciding to go to 25 x 127, for which it installed a Mauser Mk25 Mod.E cannon in the KuKa tower as an upgrade of its MARDER. Later, the upgrade was canceled and it was decided to go straight to MARDER 2 with a Rheinmetall Rh503 35 x 288 / 50 x 330 Supershot cannon, but after the fall of the Berlin Wall and the end of the cold war, MARDER 2 with its Rh503 canceled and chose a more acceptable and clearer in the best way for good design to make a good one and more and more and more 30 2 x 30 for the new PUMA BMP.
In a broad sense, 20 x 139 is currently the only projectile for older-generation machines awaiting decommissioning. The 25 x 137 ammunition is still “valid” as an acceptable compromise between performance and price, but for new-generation vehicles or re-ordered, for wheel models, low weight, compactness and cost are the main reasons. In fact, 30 x 173 was chosen as the base case when there are no valid reasons to have a smaller or larger caliber. He adopted, for example, Austrian The ULAN, Spanish PIZARRO, Norwegian CV9030 Mk1, Finnish and Swiss CV9030 Mk2, promising machines EFV US Marine Corps, the Polish Rosomak, Portuguese and Czech PANDUR II, Singapore BIONIX II, and many others. The 35 x 228 ammunition is an expensive solution, but with high performance, while the 40 x 365R has a pair of “fans” too.
The gun with external power Nexter M811 (25 x 137) was adopted for the new VBCI machine of the French army
The real way forward is quite clearly represented not by the CT 40 gun as such, but of course by the advanced technologies that it personifies. But whether financial and industrial factors will allow to realize these promising advantages and actually achieve operational status, the future will show.
Thus, it is very encouraging that ongoing work is continuing on an automatic 40-mm weapon system with CTWS (cased telescoped weapon system) telescopic ammunition developed by CTA International, as part of the WARRIOR (WCSP) BMP life extension program, for the FRES Scout reconnaissance vehicle British Army and a promising reconnaissance vehicle for the French Army. The CTWS weapon system has already fired and was tested with its original ammunition supply system, but the upcoming firing this year will demonstrate for the first time the capabilities of the CTWS, which will be installed in a full-fledged WCSP tower. However, the shooting will most likely be conducted from a stationary position, and not in motion, as representatives of Lockheed Martin UK had previously suggested.
The next step will be negotiations on the serial production of the CT gun (CTWS). BAE Systems Global Combat Systems - Munitions (GCSM), in accordance with a license issued by CTAI, recently submitted a proposal to the British Department of Defense for the production of serial ammunition through an existing supply contract for the UK MASS ammunition. The license will also be issued to Nexter Munitions for the production of mass-produced ammunition for the French arms procurement agency.