Ammunition and Weapon System

The present invention relates to a weapon and ammunition.

More particularly, the invention relates to such a system wherein a projectile is pushed by a propulsion gas coming from the combustion of a propellant charge inside a barrel closed at one end by a breech and open at the other end thereof.

Firearms include all weapons using in operation an exothermic chemical reaction. By semantic shift, the above term is often associated with weapons with a tube, the principle of which is based on the launch of a projectile inside a barrel.

In the vast majority of cases, a propellant charge is fired inside the barrel between the projectile and the breech. The generation of the propellant gases and the expansion thereof propel the projectile in an acceleration phase until same leaves the barrel.

Said phase of ballistics is called interior ballistics.

Over the years, firearms have undergone many refinements with in particular the addition of the round (sometimes also called a cartridge case) which serves to gather of the components needed for firing (primer, propellant powder, projectile) into a block called ammunition.

By construction, the barrels have a geometry quite close to a hollow cylinder the internal cross-section of which is relatively constant on the trajectory of the projectile (except for conical barrels).

When the designer of the weapon and of the ammunition thereof wants to maximize the initial velocity of the projectile, there is no element that would restrict the flow of propellant gases behind the projectile.

Thereby, the minimum diameter of the chamber and of the barrel is the minimum diameter for the passage of the projectile. Thereof is all the more true as breech loading weapons have taken precedence over muzzle loading weapons even if some uses are still common (light mortars).

An exception to the rule is the case where a relatively low initial velocity of the projectile is desired (mainly grenade launchers). In such case, the cartridge case defines two chambers, the high-pressure chamber, which contains the propellant charge and wherein combustion takes place, and a low-pressure chamber wherein expansion of the propellant gases which push on the projectile base takes place. Such construction is made necessary by the use of propellant powders that require a relatively high operating pressure for combustion to be maintained and kept repetitive from one ammunition to another.

Maximizing the initial velocity of a projectile is a constant concern of weapon designers, as thereof provides a number of advantages in the subsequent phases of ballistics. As a result, during external ballistics and for the same projectile, it is possible to obtain a “straighter” trajectory that significantly reduces sensitivity to wind, the time to impact on the target and the aiming corrections to be taken into account according to the distance, the inclination of the firing, etc.

In terminal ballistics, many weapons rely only on the kinetic effect of impact to damage or destroy the target. In such cases, maximizing the initial speed simply maximizes the energy on the target.

Thereby, research aimed at firing increasingly rapid projectiles has always been active and has provided a number of technical solutions in the field of firearms.

Thereby, at the level of the weapon and of the ammunition, three main leads are often explored:

The first lead is the increase of the duration of the projectile propulsion phase simply by increasing the length of the barrel. Same is the easiest parameter to change for the designer of a weapon and hence is the most used in the final phase of designing a weapon. Depending on the requirements governing the desired use, the length of the barrel is the subject of a compromise between the size of the weapon and the desired initial speed. The gain in the initial velocity of the projectile by increasing the length of the barrel is neither infinite nor linear, so it is sometimes necessary to resort to other tricks.

The second lead is the maximization of the pressure of the propellant gases at the rear of the projectile through the composition of the propellant powder used, the initial geometry thereof, the quantity of powder, etc. However, such method stays limited by the performance of the materials and of the manufacturing processes used for the construction of the barrels which cap the maximum internal pressure. Thereof is all the more problematic as the thermal stresses involved in each firing deteriorate the resistance of the barrel.

When the two preceding leads are already the subject of a certain optimization, the designer of the ammunition may be forced to resort to adopt a lighter projectile called a “sub-caliber” ammunition. In such case, the projectile that will impact the target is very elongate and has a diameter substantially smaller than the internal diameter of the barrel that is used in order to limit drag thereof during the external ballistics phase and concentrate the energy at impact in order to maximize the terminal effects. However, during the projectile propulsion phase, tricks are used to seal the guidance of the projectile in the barrel in order to contain the propulsion gases behind the projectile and maximize thrust during the internal ballistics phase.

Two solutions are relatively well known for achieving such results:

While it is important to minimize friction between the projectile and the barrel, it is nevertheless necessary to guarantee a good sealing so as to prevent the passage of part of the propellant gases in front of the projectile inside the barrel. When thereof is the case, the initial velocity of the projectile is greatly impacted and the wear of the barrel is accelerated. Historically, the sealing function was fulfilled by a wad placed behind the projectile (at the time of paper cartridge cases). As the means of production improved and the geometry of the barrels and of the projectiles became better controlled, said function was fulfilled by tightening and deforming the projectile (made of lead and then jacketed with copper) in the barrel. For larger caliber ammunition, it is not rare to see said function performed by a part surrounding the projectile, called belt. As a general rule, the belt is made of copper alloy or polymer to minimize friction with the barrel by means of “dry lubrication”.

More trivially, some shooters do not hesitate to use specific greases on small caliber projectiles. For firing in modern weapons, the gain linked to the use of lubricated ammunition is not obvious despite a marginal influence on certain parameters of internal ballistics. For the firing of historical weapons (black powder weapons), the interest lies mainly in the creation of a sealing of the powder against external moisture when storing a weapon containing ammunition. However, it is accepted that the protection sought with such devices relates to the interaction between the projectile and the barrel and has only a negligible effect on the thermal aspects of the barrel.

Each of such themes is well known to weapons and ammunition designers so that it is sometimes possible to find the design signature of some solutions currently in use in state-of-the-art weapons in patents dating from the 19th century. For example, it is difficult to ignore the resemblance between a current 120 mm APFSDS ammunition of the LECLERC tank and the ammunition described in the patent U.S. Pat. No. 487,125 dating from 1892. Both have semi-combustible cartridge cases with a metal base to facilitate the sealing of the chamber at the breech and the handling of the ammunition, a sub-caliber projectile thrust by a sabot system separating into three pieces at the exit of the barrel, etc. However, there is no doubt that many advances have been made between the publication of said patent and modern ammunitions. The geometry of the projectile and sabots, the materials used, the relative dimensions of certain elements, etc. are all points that have been the subject of many studies and of many innovations that allow current weapons to achieve the performance required therefrom.

Internal ballistics is the science of transmitting energy from a propellant powder to a projectile. Of course, such energy is only useful if is transmitted to the target, i.e. dissipated inside the target in order to create significant damage. The projectile is chosen to maximize the energy transfer depending on the nature of the target and on the protection applied thereto. To pierce a large armor, a long projectile with homogeneous composition provides good performance, more particularly if the impact speed is high. However, for softer and less armored targets, such a projectile is not optimal, since the projectile will travel through the target without transferring a significant part of the energy thereof to the target.

While it is obvious that the optimization of each of the three main parameters of interior ballistics makes it possible to achieve a quite remarkable level of performance, some physical phenomena greatly limit the level of performance accessible to such technology.

From a certain length of barrel on, the pressure of the propellant gases on the base of the projectile is no longer sufficient to accelerate the projectile. Beyond such barrel length, the projectile will be slowed down by the pressure-drop forming behind same so that increasing the barrel length only reduces the performance of the weapon. Such problems affect much more small-caliber weapons than medium and large-caliber weapons where the optimization of certain parameters of the powder charge means that the constraints of bulkiness of the weapon (overall length, mass, inertia at aiming, etc.) will be reached before the overexpansion of the propulsion gases is the limiting phenomenon.

The maximum pressure attainable in the barrel also quickly finds an “absolute” limit due to the performances of the materials used. Initially, it could be tempting to consider the problem starting from the proportionality between the maximum acceptable pressure in a thin-walled tube and the thickness of the tube, however it means to forget that for many weapons, the thickness of the wall of the barrel is on the same order of magnitude as the caliber of the ammunition and that, consequently, the hypothesis of thin walls is not satisfied.

Under such conditions, the main parameter for increasing the maximum pressure withstood by the barrel is the elastic (and fracture) limit of the material used after heat and mechanical treatment. Such limit is all the lower as is affected by the thermal regime of the barrel during the use thereof (repeated and close firing for machine guns and automatic guns), but also by the limited choice of suitable material due to the desired behavior in case of obstruction (ductile behavior is preferable, in order to minimize the projection of fragments in case of destruction of the barrel).

Thereby, work concerning the design and manufacture of “composite” barrels resulting from the assembly of a plurality of materials with different properties is relatively frequent, and, although there is no universal solution, some combinations are quite frequent in certain uses (cobalt alloy core crimped with steel for machine gun barrels, etc.).

Finally, even the use of a sabot system for the propulsion of a sub-caliber projectile finds a limit due to the maximum rate of expansion of the propulsion gases inside the barrel. It is generally accepted that the maximum speed for conventional firearms is on the order of 2300 m/s. In practice and operationally, the order of magnitude of the initial speeds reached by firearms is on the order of 1800 m/s.

To achieve higher speeds, some technical solutions have been developed or are still being studied.

Thereby, there are light gas barrels that use helium or hydrogen compression in a secondary chamber placed between the combustion chamber and the projectile as an intermediate step in propellant the projectile.

Other proposals were described in the documents DE 1428634, DE 1280092 and DE 2201693.

Similarly, there are many attempts, with various degrees of success, of magnetic, electric, electrothermal, purely mechanical, etc. barrels. While same often give promising results in terms of the initial velocity of the projectile, the practical constraints of the terrain mean that such solutions do not find a concrete and operational application. In fact, the search for new and better ammunition is always active.

Such is the goal of the present application.

To this end, the subject matter of the invention is an ammunition and weapon system, wherein a projectile is thrust by a propellant gas coming from the combustion of a propellant charge inside a barrel closed at one end by a breech and open at the other end thereof, characterized in that at least a part of the propulsion gases generated by the combustion of the propellant charge passes through a nozzle bringing the propulsion gases to a supersonic speed, placed in the barrel, between the breech and the projectile, and having a converging portion, a throat and a diverging portion, one after the other toward the open end of the barrel.

According to other possible features of the system according to invention, taken alone or in combination:

Indeed, the figures illustrate different embodiments of a system according to the invention.

In fact, the system uses a sub-caliber projectile guided by at least one degradable sabot inside a barrel, at least a portion of which has a conical cross-section.

In the figures, the references:

The caliber of the projectile is then consistent with the diameter of the barrel at the muzzle of the latter, but the inner diameter of the barrel near the chamber is substantially greater than the caliber of the projectile, in order to accommodate the passage of the sabot.

The sabot is not so much a piece as such as a degradable joint between the projectile and the barrel. The sabot will be progressively trimmed during the passage of the projectile into the conical portion of the barrel by the variation in the diameter of the barrel and then degraded by the temperature of the propulsion gases thrusting on the base of the projectile.

The aim is that, in addition to carrying out the functions of guiding the projectile in the barrel, of sealing between the barrel and the projectile, and of maximizing the thrust surface of the propulsion gases during the internal ballistics phase, the transfer in the way such as to form the degradable sabot to the internal face of the conical portion of the barrel produces a protective layer serving to limit, at least in part, the heat transfers between the propulsion gases and the barrel. Such function is achieved by degrading the material acting as a degradable sabot at a temperature lower than the temperature of the propellant gases.

The material chosen for the degradable sabot should thus meet a certain number of criteria. The density of the material used and the quantity of material used have to allow the area density of the sabot to be lower than the area density of the projectile alone so that the under-calibration of the ammunition results in an improvement in performance at the muzzle. The mechanical strength of the material of the sabot should be sufficient to allow the transmission of the additional thrust to the projectile, but also sufficiently low for friction against the internal wall of the barrel to lead to an ablative wear of the sabot. The combustion of the residues resulting from the deterioration of the sabot during firing should be as complete as possible and thus take place while the projectile has not yet left the barrel. The combustion temperature of the sabot material should be as low as possible in order to maximize the thermal protection of the barrel.

It may be thereby envisaged that sabot is composed of at least one of the following materials: nitrocellulose, nitroglycerin, shellac, gum arabic, gum tragacanth, gelatin, dextrin, asphalt, polybutadienes, polyesters, polyurethanes, polyfluoroelastomers, silicones, polyvinyls, graphite, potassium, centralite, camphor, phthalic ester, nitroguanidine, nitroaminoguanidine, triaminoguanidine nitrate, N-butyl-N(2 nitroxyethyl).

The variation in the diameter of the barrel is continuous, progressive, but not necessarily linear. A final portion of the barrel, at the muzzle, may have the diameter needed for bearing directly on the projectile and impart same a rotation needed for the gyroscopic stabilization thereof.

For the designer of a firearm and of the ammunition thereof, the conical barrel technique and the saboted ammunition technique are two competing technologies belonging to the category of sub-caliber weapons and ammunition. In both cases, the dilemma of maximizing the impact velocity between internal and external ballistics is to be solved.

Indeed, to maximize the velocity at impact on the target, at identical projectile masses, the maximum cross-section [maître-couple] of the projectile (maximum surface area of the projectile cross-section along the main axis thereof) is a key parameter in each of the phases of ballistics but has an inverse influence during internal ballistics and external ballistics.

During internal ballistics, a large maximum cross-section makes possible a stronger acceleration of the projectile due to the large surface area on which the pressure of the propulsion gases is applied. However, a strong maximum cross-section also considerably increases the drag force to which the projectile will be subjected during the external ballistics phase, which increases the energy loss, more particularly for distant targets. On the other hand, a projectile with a small maximum cross-section will lose less energy during the free flight phase. However, the propulsion phase of the projectile will be negatively affected by such choice, which will limit the initial velocity of the projectile.

The “resolution” of such dilemma by a compromise on the maximum cross-section of the projectile generally results in an initial velocity of less than 1000 m/s for a barrel length acceptable for a standard weapon. However, in the case of weapons specialized in penetrating protected targets, a higher initial speed is often required. In such cases, the solution of a compromise is no longer privileged, and the designer then turns to adopting a sub-caliber ammunition system.

Historically, the use of a projectile with variable maximum cross-section in a conical barrel is a solution that has rarely been adopted due to the complexity of implementation (making and maintenance) and the low performance gain associated thereto. Indeed, the need to gradually vary the internal diameter of the tube to pass from a large maximum cross-section in the initial phase of internal ballistics to a weak maximum cross-section at the muzzle of the barrel implies that the solution has an effect only in the beginning of the thrust phase. Thereby, the gain in performance is relatively limited and the applications where the initial velocity of the projectile exceeds 1500 m/s, are rare. Nevertheless, it should be noted that such solution also has the advantage of making possible gyro-stabilized ammunitions to be fired without any fins.

The other big family of sub-calibration solutions for ammunition is the use of a so-called “sabot” ammunition where the projectile with small maximum cross-section is clamped by a sabot providing sealing with the barrel during the internal ballistics phase. The main advantage of such solution lies in the use of a large maximum cross-section over the entire length of the barrel, which maximizes the thrust on the projectile until the exit from the barrel. However, such method also affects the efficiency of propulsion, since a part of the energy is used to accelerate the sabot, the mass of which can be of the order of 30% of the mass of the projectile. Furthermore, the sabot system is rarely used in conjunction with a rifled barrel. Indeed, the non-concentricity of the projectile in the sabot causes a precession movement which will only be dampened by the presence of a stabilizing fins moving the center of drag behind the center of gravity of the projectile. Consequently, sabot ammunition is most often used in conjunction with a smooth-core barrel, the projectile being mainly stabilized by fins having a certain incidence with respect to the axis of the projectile in order to give same additional gyroscopic stability by rotating the projectile in the initial phase of external ballistics (transient ballistics).