AMMUNITION AND WEAPON SYSTEM

Description

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:

• • 1) The use of a deformable projectile inside a conical barrel with an internal diameter substantially greater on the chamber side than on the muzzle side (such as the German 28-20 mm barrel). In such case, the sealing between the projectile and the barrel is obtained by a deformable portion of the projectile which will be tightened around the core of the projectile progressively as same travels the length of the barrel.
  • 2) The use of an intermediate sabot between the projectile and the barrel during the internal ballistics phase and separating from the projectile at the exit of the barrel. The sabot is made of a low-density material such as aluminum or some polymers. The sabot may be in one piece pressing on the rear face of the projectile (SLAP ammunition) or in a plurality of parts joined around the projectile by belts and releasing the projectile by moving radially apart (APFSDS ammunition).

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:

• • the nozzle is formed inside a chamber which is removable from the barrel so as to make possible the loading of the propellant charge by the rear end and the loading of the projectile by the front end of the chamber;
  • the nozzle is formed inside a cartridge case forming an ammunition grouping the projectile and the propellant charge before firing;
  • the projectile is positioned relative to the barrel before the firing, by matching between the shape of a projectile base or one or a plurality of sabots and a portion of the nozzle;
  • the propellant charge includes a priming composition, a fast-burning charge and a slow-burning charge;
  • at least one part of the barrel has a conical cross-section and the projectile is associated with at least one sabot which is degradable when the sabot is moved into the conical section part of the barrel;
  • the sabot is made of a material deposited on the barrel progressively as same moves therethrough, in order to form a thermal protection layer of the latter which is then discharged;
  • the discharge of the protective layer from the barrel is obtained:
    • either by a change of phase, i.e. liquefaction, evaporation or sublimation, of the material forming the sabot, or
    • same may result from a reaction of the material forming the sabot with the propellant gases from the combustion of the propellant charge,
    • either self-burning of the material of the sabot, or
    • a combination of at least two of the three methods described;
  • the 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) nitramine;
  • the barrel comprises a portion with a conical section, followed by a portion with a rifled straight section, the projectile being guided by the sabot in the conical section of the barrel and by direct contact between the projectile and the barrel in the straight section of the barrel;

The invention will be better understood upon reading the following description, given only as an example and making reference to the enclosed drawings, wherein:

FIG. 1 is a sectional view of an embodiment of a system according to the invention, with an ammunition in firing position;

FIG. 2 is a sectional view of said system shown with the ammunition being fired;

FIG. 3 is sectional view on an enlarged scale of a portion of the system according to the invention;

FIG. 4 is a sectional view on an enlarged scale of portion of another embodiment of a system according to the invention with an ammunition in the loading position;

FIG. 5 is a sectional view on an enlarged scale of a portion of the other embodiment of the system according to the invention with an ammunition being fired; and

FIG. 6 is a sectional view of an embodiment of an ammunition of a system according to the invention.

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:

• • 1 identifies the breech of a barrel,
  • 2 identifies a combustion chamber which may be removable from the barrel so as to make possible the loading of a propellant charge from the rear end and the loading of a projectile from the front end of the chamber;
  • 3 refers to a nozzle with a converging portion 3a, a throat 3b and a diverging portion 3c, one after the other toward the open end of the barrel,
  • 4 identifies the barrel with a portion with conical section 4a and a portion with straight section 4b, e.g. with a rifled section,
  • 6 identifies the muzzle of the cannon,
  • 7 identifies a projectile with a projectile base 7a and a projectile warhead 7b,
  • 8 identifies a degradable sabot,
  • 9 identifies a protective layer of the barrel,
  • 10 identifies a propellant charge with a fast-burning charge 10a, a long burning charge 10b and a priming composition 10c,
  • 11 identifies the shock wave,
  • 12 identifies to propellant gases, and
  • 13 identifies an ammunition with a cartridge case 13a and a primer 13b.

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).

In fact, two sabot technologies are implemented: a monolithic sabot thrusting the projectile from the rear and positioning the projectile via lateral petals that will move apart at the exit of the barrel. Such ammunition is called SLAP for Saboted Light Armor Penetrator. The other solution consists of a plurality of sabots taking the form of a portion of a hollow piece of revolution which clamps the projectile laterally. The sabots separate from the projectile at the exit of the barrel under the effect of aerodynamic forces and of inertia. The resulting ammunition is referred to by APDS for Armor Piercing Discarding Sabot when the projectile is without stabilizing fins, and APFSDS for Armor Piercing Fin-Stabilized Discarding Sabot when stabilizing the projectile is obtained by rear fins.

A solution such as the solution proposed by the invention consisting of a mixture between the two solutions (conical barrel and saboted projectile) is not one of the options that may be used when designing a new weapon because of the cumulative disadvantages (reduction of the thrust surface as the projectile advances in the barrel and increase of the mass propelled by a sabot mass) without there being any cumulative advantages. Thereby, no obvious gain of performance is expected by the designer while the complexity of the development is glaring.

The evolution of the needs in the field of firearms, more particularly the requirements relating to armor penetration, are pushing weapons and ammunition designers into a race for performance which shows in adopting strong initial speeds. However, to meet customer expectations, the trend is currently to increase pressure in the barrels of small and medium caliber weapons. However, certain limitations are clearly achieved with regard to the choice of materials and the resistances thereof. Thereof is all the more glaring in the case where the weapon must be able to fire at a high rate over a prolonged period of time. In such case, it is necessary to take into account the decrease in the strength of the material used for the barrel due to the rise in temperature of the barrel, which implies a high limit to the operating pressure of an ammunition which is currently on the order of 600 MPa for steel barrels. The use of such a high operating pressure involves severe limitations on the life of the barrel as well as restrictions on firing regimes for weapons which can fire at a high rate.

In order to achieve a substantial gain in performance without being penalized by the capping of the maximum acceptable pressure by the barrel, the question of the use of sub-caliber ammunition should be reconsidered.

The practicality of gyroscopic stabilization advocates for the use of the conical barrel method combined with a deformable projectile. Thereof is all the more obvious since the method is, at first glance, more suitable for mass production compared to the production of a projectile-and-sabot assembly. Usually, such solution is not retained because a deformable projectile does not make a good penetrator. It is therefore necessary to resort to a two-part projectile: a deformable body and a hard core which will serve as a penetrator. It is usually such constraint that pushes the weapon designer to turn to the use of a sabot and thus to leave the conical barrel solution in favor of adopting an APDS projectile.

Nevertheless, by continuing the study of a conical barrel combined with the use of an APDS ammunition, a weapon designer realizes that the accumulation of expected defects shows in the following form: the taper of the barrel reduces the thrust surface of the combustion gases on the base of the projectile, adopting a sabot reduces the thrust efficiency by the addition of a propelled mass the energy of which is not transmitted to the target. The new idea lies in the fact of no longer considering that the sabot has a fixed mass, but that the mass thereof can decrease as and when the sabot is made of a material which can degrade/erode on the walls of the cannon.

If an erosion of the degradable sabot related to the taper of the barrel is considered, it is observed that the mass of the accelerated assembly (projectile and sabot) decreases as the projectile advances and gains speed. Thereby, the efficiency of the transfer of energy from the propulsion gases to the projectile improves, because there is less and less mass of degradable sabots to propel. In such configuration, the penalty related to the use of a sabot is thereby reduced even if same is replaced by the penalty related to the reduction of the thrust cross-section of the gases on the projectile-and-sabot assembly. Consequently, the level of performance attainable by such method is, at a minimum, comparable to the level of performance attainable by the already known conical barrels.

The material that will be detached from the sabot by the abrasion thereof inside the conical barrel then forms a layer on the inner wall of the barrel. Such layer has to be evacuated, preferably between each firing, so that the performance of the weapon is constant over time. If the risk of obstruction is relatively low, a pronounced fouling of the barrel is considered a negative point for the maintenance of a weapon, more particularly when the weapon operates repeatedly via an automatic system using a borrowing of gas in the barrel. Thereby, it becomes necessary to manage the discharge of the sabot in a form other than a support for the projectile.

One solution is to choose the material forming the sabot as indicated hereinabove, giving same the properties needed for the discharge thereof in the form of gas at the same time as the propellant gases coming from the combustion of the propellant charge. Thereof implies that the material used for the degradable sabot should have a vaporization or sublimation temperature lower than the temperature of the propellant gases during firing. A large number of polymers fall into such category, waxes are also fairly good candidates.

Another possibility is to make the degradable sabot material interact with the propellant gases coming from the combustion of the propellant charge in the form of a chemical reaction (acid-base or redox). For example, the oxygen balance of the propellant charge may be large enough that the excess oxygen can react with the material of the degradable sabot to form a gas that mixes with the propellant gases and is thus discharged like the latter. Materials with properties conducive to such type of strategy are polymers composed mainly of carbon chains, graphite, etc. Materials that are difficult to oxidize or the oxidation residues of which are not in the gaseous state at the temperature and pressure present in the barrel are not good candidates for the manufacture of a degradable sabot.

Finally, it is possible to use a material containing both the oxidant and the reducer, i.e. a propellant, for the creation of the degradable sabot. In such case, the advantage is that the combustion of the material used as a degradable sabot and then as a protective layer is ensured by exposure to the temperature and to the pressure of the propellant gases. Another advantage is that the energy contained in the degradable sabot is added to the energy of the propellant charge in the form of an increase in the amount of propellant gas in the barrel behind the projectile as well as an increase in the temperature of the propellant gas in the barrel.

In practice, mechanical stresses (resistance of the sabot to acceleration, adhesion of the sabot to the projectile, coefficient of friction between the barrel and the sabot material, etc.) also play an important role in the choice of material for the degradable sabot. Therefore, the use of a combination of different materials in the form of a composite, each component of which falls into at least one of the aforementioned categories, is a perfectly suitable solution for the production of a degradable sabot. Among composite solutions, compositions similar to same used in powder rocket engines, combining an oxidizer and a reducer held together by a resin, form a family of promising solutions.

It is notable that leaving a layer of material inside the barrel during the passage of the projectile can also have a secondary (even temporary) insulating function between the inner wall of the barrel and the hot propulsion gases. Indeed, the fact that the residual layer, known as the protective layer, after the passage of the sabot is only apt to withstand a moderate temperature before sublimating and, possibly, reacting chemically, creates a form of temporary barrier between the propulsion gases and the internal surface of the barrel. Therefore, the inner wall of the barrel is not subjected to a temperature higher than the sublimation temperature of the degradable sabot material until same has been completely detached from the wall. It is possible to maximize such effect by selecting the degradable sabot material in relation to the sublimation temperature thereof, or by incorporating reactive additives acting as moderators in propellants (graphite, potassium, centralite, camphor, phthalic ester, etc.), or by using at least one other stabilizer and flame temperature reducer such as nitroguanidine, nitroaminoguanidine, triaminoguanidine nitrate or N-butyl-N(2 nitroxyethyl) nitramine.

It is important to note that the insulation effect of the inner wall of the barrel is maximum for a short barrel with a rapid reduction of the inner section. Such geometry is generally associated with a compact and light weapon, which is a feature common to many weapons firing in bursts of variable lengths at relatively high rate. Such weapons generally derive the effectiveness thereof from a saturation effect of the target area and not from the individual power of each projectile launched. In such case, the use of a combination between a barrel with high-tapering and a degradable sabot ammunition makes possible a sure reduction in the thermal stress of the equivalent performance barrel. As a result, the weapon designer will be able to afford some reduction in the wall thickness of the barrel in order to reduce the mass of the weapon, the elimination of a rapid barrel replacement system (usually present on infantry machine guns) or an increase in the acceptable firing regime if the mass of the weapon is not a problem. On the other hand, weapons combining high power of each firing and precision are generally already equipped with long and large diameter barrels. Thereby, there is no particular penalty for such weapons due to the adopting of a degradable sabot ammunition associated with a barrel of moderate taper.

In any case, the discharge of the protective layer from the barrel is e.g. obtained:

• • either by a change of phase, i.e. liquefaction, evaporation or sublimation, of the material forming the sabot, or
  • same may result from a reaction of the material forming the sabot with the propellant gases from the combustion of the propellant charge,
  • either self-burning of the material of the sabot, or
  • a combination of at least two of the three methods described.

Another constraint to be taken into account is the need to keep the projectile coaxial with the barrel while the latter is accelerated by the sabot in the conical section of the barrel.

The concentricity of the projectile in the barrel does not rise any particular problem, as the breaking of contact on one side of the barrel automatically causes an imbalance of the radial forces of the barrel on the degradable sabot which will be redirected to a position of equilibrium in the center of the barrel. In such case, it is the taper of the barrel that ensures the permanent recentering of the projectile in the barrel.

The coaxiality of the projectile in the barrel is at first glance more problematic. Two scenarios are to be considered.

In the case of a long guiding of the projectile in the barrel, i.e. a contact length between the degradable sabot and the barrel substantially greater than the outside diameter of the degradable sabot, it is preferable that the front and rear faces be substantially more resistant than the core of the sabot. Thereby, the phenomenon of recentering the projectile in the barrel applies independently to the front of the degradable sabot and to the rear of the degradable sabot, which provides the coaxiality of the projectile with respect to the barrel.

However, it is not always possible to provide long guiding between the degradable sabot and the conical barrel. In such case, the condition of coaxiality of the projectile in the barrel lies in the rearward positioning of the center of gravity of the degradable projectile-and-sabot assembly with respect to the zone of contact between the sabot and the barrel. Indeed, if such condition is fulfilled, when the projectile is no longer coaxial with the barrel, the center of gravity of the projectile-and-degradable-sabot assembly shifts to the “ahead” side by the rotation of the projectile-and-degradable-sabot assembly around the center of the guiding. The distribution of the mass of the degradable projectile and sabot assembly on the thrust surface of the propulsion gases is modified with a higher mass on the “ahead” side and a lower mass on the “behind” side. Since the thrust pressure of the propulsion gases is relatively uniform, the acceleration on the “behind” side will be greater than same on the “ahead” side, which will result in bringing the projectile into a coaxial position with the barrel.

It is interesting now to note that the appropriate shape for the base of the degradable sabot in order to fulfill the last condition of stability is quite close to a cone pointing toward the breech of the weapon. Such shape makes it possible to satisfy the condition of coaxiality by short guiding when the maximum cross-section of the barrel is large (close to the breech) and to progressively switch to long guidance progressively as the diameter of the degradable sabot decreases, due to the tapering of the barrel.

It will be noted that such shape can match a nozzle shape as described thereafter. Two obvious advantages can be derived from such configuration.

The first advantage relates to the rigidity of the ammunition for the manipulations of guiding and chambering the ammunition in the barrel. In fact, it is thereby possible to reduce the transmission by the degradable sabot of lateral forces to the tip of the projectile during such operations by working the shape of the projectile base so that there is contact between the projectile base and the throat and/or diverging portion of the nozzle of the cartridge case.

The second advantage of such configuration is the industrialization of ammunition. Indeed, in a configuration wherein the base of the projectile is in contact with the throat and/or the diverging portion of the nozzle of the case, the production of the degradable sabot is possible by injecting the material selected for the degradable sabot into an impression positioning the projectile and being closed by the cartridge case.

Another point of the system according to the invention relates to the presence, during the thrust phase of the internal ballistics, of a separation between the chamber, the place of combustion of the propellant charge, and the projectile. Such separation is made by means of a nozzle for the passage of gases at a supersonic speed inside the barrel.

To this end, a plurality of architectures is possible depending on the nature of the weapon desired and of the accepted disadvantages:

If the weapon in question is a muzzle barrel reloading weapon, the nozzle may be permanently fixed and formed directly by the barrel. In such case, the propellant charge can be installed through the muzzle of the barrel if the propellant charge is in the form of a powder sufficiently fine to be added into the chamber through the nozzle and the throat. Preferably, the propellant charge is added into the chamber through the breech, in the form of pellets or a blank cartridge. The projectile is always inserted through the muzzle of the cannon. All types of conventional or sub-calibrated projectiles are compatible with such configurations.

If the weapon is necessarily exclusively powered by the breech, two solutions are available to the weapon designer: the separate loading of the propellant charge into the chamber and the projectile into the barrel on the one hand, or the integration of the nozzle inside the cartridge case without any particular modification to be made to the weapon. The latter configuration is preferred because of the practicality thereof with regard to operations of loading, discharge of fire waste, unloading of the weapon or cleaning of the system.

Thereby, the nozzle may be formed inside a chamber which is removable with respect to the barrel so as to make possible the loading of the propellant charge by the rear end and the loading of the projectile by the front end of the chamber, or the nozzle may be formed inside a cartridge case forming an ammunition grouping the projectile and the propellant charge together before firing. In addition, the projectile can be placed inside the ammunition cartridge case by matching between the shape of a base of the projectile or of one or a plurality of sabots and a portion of the nozzle as long as the ammunition is assembled.

The modeling of the internal ballistics of firearms is well known and is based on a set of equations for determining the change of certain parameters in order to deduce therefrom the change of the velocity and of the position of the projectile during firing. One of the equations represents the energy balance inside the barrel and highlights the partial transfer of the energy released by the propellant charge into the kinetic energy of the projectile. The two phenomena limiting the transfer of energy are none other than the non-transformation of a part of the thermal energy of the propulsion gases (which acts as a form of potential energy reserve allowing the projectile to continue to be propelled in the barrel, while the combustion of the propellant charge is complete), and the movement of the propulsion gases (energy which is lost).

If one sticks to such model, a trick inside the barrel leading to the increase in the velocity of the propulsion gases is necessarily harmful to internal ballistics since same increases the kinetic energy of the same propulsion gases and thus reduces by the same amount the energy available for the projectile. Therefore, the addition of a reduced passage section for the propulsion gases, compared to the passage section of the projectile in the barrel, at the outlet of the chamber is considered a design error with regard to the creation of a high-velocity ammunition.

However, thereof would mean also to forget that the amount of energy available is concretely limited with regard to the amount of propellant used (and thus to the capacity of the chamber). Another more limiting factor for the performance of a barrel-ammunition pair is the maximum pressure that the barrel can withstand. Thereby, a loss of efficiency in a phase of priming and the beginning of propulsion of the projectile is not necessarily a handicap for the performances of the barrel-munition pair if another phenomenon makes it possible to override the limitations of maximum pressure tolerable by the barrel.

In the barrel, the static pressure exerted on the inner walls of the barrel is related to the static pressure at the breech and to the velocity of the propulsion gases at the location considered of the barrel. The faster the propulsion gases, the lower the static pressure exerted on the walls of the barrel. In a traditional barrel, thereof results in a decrease in the maximum pressure reached progressively as one moves toward the muzzle of the barrel. Thereof is explained by the LAGRANGE hypothesis which indicates that the variation in gas velocity is linear between the breech and the base of the projectile. Such phenomenon is all the more pronounced since, very often, the combustion of the propellant powder is complete while the projectile has not yet exceeded half the length of the barrel (especially for long-barrel shoulder weapon), which means that the peak of total pressure available (static pressure at the breech) is already exceeded while the projectile is still in the barrel.

For weapons suitable for fast projectile firing, the barrel is formed of a tube the wall thickness of which is often close enough to, or even greater than, the diameter of the projectile. Thereof means that the internal stress that can be sustained by the barrel during firing is less and less correlated with the increase in the external diameter of the tube (hypothesis of hollow cylinders of small thickness), but that the limiting factor becomes the limit to the fracture of the material used for the barrel core. In fact, the limit to the maximum operating pressure of ammunitions is directly related to innovation in the field of high-tenacity materials, including high-temperature materials, and the failure mode of which is compatible with the safety of the weapon. Indeed, in case of obstruction, a barrel that bursts (which opens in a crack without creation and dispersion of fragments) is preferable to a bursting behavior (brittle fracture with projection of fragments).

Consequently, there is a major interest, for a weapon designer, in seeking to reduce the static pressure applied to the internal walls of the barrel while maximizing the pressure undergone by the base of the projectile in order to maintain, or increase, the performances of the weapon-munition pair. To this end, the modification of the distribution of the velocity of the propulsion gases between the breech and the base of the projectile is an interesting option that has unfortunately not been studied.

To achieve a profound modification of the velocity field in the propulsion gases between the breech and the base of the projectile, it is necessary to place a firework inside the barrel which will have the function of increasing the velocity of the propulsion gases and thus of reducing the pressure on the inner walls of the barrel. Since the modification of the flow of propulsion gas inside the barrel occurs mainly downstream of the tricks, it is necessary that the tricks accelerating the propulsion gases be placed as close as possible to the breech so that most of the barrel benefits from the advantages granted.

The artifice that allows the transition between a high-pressure tank on the side of the breech (called chamber) and the barrel, where the pressure is lower and the velocity of the propulsion gases is particularly important, is nothing else than a nozzle. Same is characterized by a throat, the narrowest passage through which the propellant gases pass, a converging portion par accelerating the propellant gases to a sonic speed and a diverging portion bringing the propellant gases to a supersonic speed.

In the initial state, the entire propellant charge is in the chamber which is closed by the nozzle throat and the projectile. When the ammunition is fired, a priming phase begins that can be modeled in the same way as the internal ballistics of a traditional firearm of the same type. It is nevertheless necessary to take into account the head loss during the passage through the nozzle.

The end of the priming phase is characterized by a speed of passage of the propellant gases through the throat at the speed of sound in the same gas. At such moment, a shock wave is created at the throat and decouples the chamber, where there is a high static pressure forcing combustion of the still unburned powder, from the barrel, wherein the nozzle ejects the product of the combustion of the propellant charge at a supersonic speed and a lower static pressure.

The propulsion gases are compressed again at the base of the projectile which thereby continues the propulsion phase thereof in the barrel. The pressure to which the projectile base is subjected is linked to two components: The static pressure at the nozzle outlet and a dynamic component linked to the difference between the speed of ejection of the propulsion gases at the nozzle and the velocity of the projectile in the barrel. Thereby, the pressure applied to the inner walls of the barrel is substantially lower than the pressure exerted in the chamber, with a distribution passing through a minimum at the outlet of the nozzle and a progressive recompression toward the pressure at the base of the projectile.

The projectile can then be placed inside the ammunition cartridge case by matching between the shape of a base of the projectile or of one or a plurality of sabots and a portion of the nozzle as long as the ammunition is assembled.

The constraints of construction and operation of the barrel-ammunition pair mean that the thickness of the barrel material is significantly greater on the breech side than on the muzzle side of the barrel. In fact, it is often easier, and less expensive in terms of performance, to reinforce the chamber than the entire barrel. The decrease in static pressure inside the barrel is also accompanied by a decrease in the temperature of the gases in the barrel.

In order to facilitate the supersonic speed of the combustion gases at the nozzle throat, it is preferable to use a method of increasing the velocity of the projectile by a method of sub-calibration of the projectile with respect to the barrel. Insofar as the goal is to obtain a decoupling of the chamber as quickly as possible, the sabot technique is as well suited as the deformable projectile technique in a conical barrel. However, it should be noted, that the technique of the projectile with degradable sabot accelerated by a conical barrel provides certain synergies if combined with adopting a nozzle in the barrel.

Other embodiments can, of course, be envisaged.