Weapon and ammunition system

Abstract

This ammunition and weapon system, in which a projectile (7) is thrust by a propellant gas obtained from the combustion of a propellant charge (10) inside a barrel (4) that is closed at one end by a breech (1) and open at its other end, is characterized in that at least one portion of the barrel (4) has a conical cross-section (4a) and in that the projectile (7) is associated with at least one sabot (8) which is degradable during the movement thereof in said portion of the barrel having the conical cross-section.

Description

[0001] DESCRIPTION

[0002] TITLE: WEAPON AND AMMUNITION SYSTEM

[0003] The present invention relates to an ammunition and weapon system.

[0004] More particularly, the invention relates to such a system in which a projectile is pushed by a propulsion gas resulting from the combustion of a propellant charge inside a barrel closed at one end by a breech and open at its other end.

[0005] Firearms are a term used to describe all weapons that use an exothermic chemical reaction in their operation. By semantic shift, this term is often associated with barrel-fired weapons, the principle of which is based on the launching of a projectile inside a barrel.

[0006] In the vast majority of cases, a propellant charge is ignited inside the barrel between the projectile and the breech. The generation of propellant gases and their expansion propel the projectile into an acceleration phase until it leaves the barrel.

[0007] This phase of ballistics is called internal ballistics.

[0008] Over the years, firearms have undergone many refinements, including the introduction of the cartridge case (sometimes also called a case), which allows the components necessary for firing (primer, propellant powder, projectile) to be assembled into a block called ammunition.

[0009] By construction, the guns have a geometry fairly close to a hollow cylinder whose internal section is relatively constant over the trajectory of the projectile (except for conical guns).

[0010] When the designer of the weapon and its ammunition wishes to maximize the initial velocity of the projectile, there is nothing that can restrict the flow of propellant gases behind the projectile.

[0011] Thus the minimum diameter of the chamber and the barrel is the minimum diameter allowing the passage of the projectile. This is all the more true since breech-loading weapons have taken over from muzzle-loading weapons, even if certain uses are still common (light mortars).

[0012] An exception to this rule is the case where a relatively low initial velocity of the projectile is desired (mainly grenade launchers). In this case, the cartridge case draws two chambers, the high pressure chamber, which contains the propellant charge, and in which combustion takes place, and a low pressure chamber in which the expansion of the propellant gases which push on the base of the projectile takes place. This construction is made necessary by the use of propellant powders which require a relatively high operating pressure so that combustion is maintained and repetitive from one ammunition to another.

[0013] Maximizing the initial velocity of a projectile is a constant concern for weapons designers, as it provides a number of advantages in the subsequent phases of ballistics. During external ballistics and for the same projectile, this allows for a "straighter" trajectory which significantly reduces sensitivity to wind, the time to impact on the target and the aiming corrections to be taken into account depending on the distance, inclination of the shot, etc.

[0014] When it comes to terminal ballistics, many weapons rely solely on the kinetic effect of impact to damage or destroy the target. In these cases, maximizing muzzle velocity simply maximizes the energy delivered to the target.

[0015] Thus, research aimed at firing increasingly faster projectiles has always been active and has provided a number of technical solutions in the field of firearms.

[0016] So at the level of the weapon and the ammunition, three main avenues are often explored:

[0017] The first approach is to increase the duration of the projectile's propulsion phase simply by increasing the barrel length. This is the simplest parameter for a weapon designer to modify and, consequently, it is the most used in the final phase of weapon design. Depending on the constraints governing the desired use, the barrel length is subject to a compromise between the weapon's bulk and the desired initial velocity. The gain in initial velocity of the projectile by increasing the barrel length is neither infinite nor linear, so it is sometimes necessary to resort to other tricks.

[0018] The second approach is to maximize the pressure of the propellant gases at the rear of the projectile through the composition of the propellant powder used, its initial geometry, the quantity of powder, etc. This method, however, remains limited by the performance of the materials and manufacturing processes used to build the guns, which limit the maximum internal pressure. This is all the more problematic since the thermal stresses involved in each shot deteriorate the gun's strength.

[0019] When the two previous tracks are already the subject of a certain optimization, the designer of the ammunition may be obliged to resort to the adoption of a lightened projectile called "sub-caliber". In this case, the projectile which will impact the target is very elongated and has a diameter significantly smaller than the internal diameter of the barrel which is used in order to limit its drag during the external ballistic phase and concentrate the energy on impact to maximize the terminal effects. However, during the propulsion phase of the projectile, devices are used to seal the guidance of the projectile in the barrel in order to contain the propulsion gases behind the projectile and maximize the thrust during the internal ballistic phase.

[0020] Two solutions are relatively well known for achieving these results:

[0021] 1) The use of a deformable projectile inside a conical barrel having a significantly larger internal diameter on the chamber side than on the muzzle side (such as the German 28-20mm cannon). In this case, the seal between the projectile and the barrel is achieved by a deformable portion of the projectile which will be tightened around the core of the projectile as it travels the length of the barrel.

[0022] 2) The use of an intermediate sabot between the projectile and the barrel during the internal ballistic 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 certain polymers. It can be a single piece pressing on the rear face of the projectile (SLAP ammunition) or in several parts joined around the projectile by belts and releasing it by moving radially apart (APFSDS ammunition).

[0023] While it is important to minimize friction between the projectile and the barrel, it is nevertheless necessary to ensure a good seal so as to prevent part of the propellant gases from passing in front of the projectile into the barrel. When this is the case, the initial velocity of the projectile is greatly impacted as well as the wear of the barrel is accelerated. Historically, the sealing function was fulfilled by a wad placed behind the projectile (in the era of paper cartridges). As production methods improved and the geometry of barrels and projectiles became better controlled, this function was fulfilled by the tightening and deformation of the projectile (made of lead then jacketed with copper) in the barrel. For larger caliber ammunition, it is not uncommon to see this function performed by a part surrounding the projectile called a belt.Typically, the belt is made of copper alloy or polymer to minimize friction with the barrel through "dry lubrication."

[0024] More anecdotally, some shooters do not hesitate to use specific greases on small caliber projectiles. For shooting in modern weapons, the gain linked to the use of lubricated ammunition is not obvious despite a marginal influence on certain parameters of the internal ballistics. For the shooting of historical weapons (black powder weapons), the interest lies mainly in the creation of a seal of the powder with respect to external humidity during the storage of a supplied weapon. It is however admitted that the protection sought with these devices concerns the interaction between the projectile and the barrel and have only a negligible effect on the aspects linked to the thermal of the barrel.

[0025] US 4126955 and DE 102006056662 propose approaches in this direction.

[0026] Each of these themes is well known to weapon and ammunition designers, so much so that it is sometimes possible to find the conceptual signature of certain solutions currently in use in state-of-the-art weapons in patents dating back to 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 US patent 487,125 dating from 1892. Both have semi-combustible 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 pushed by a sabot system separating into three pieces at the exit of the barrel... Yet, there is no doubt that many advances have been made between the publication of this patent and modern ammunition.The geometry of the projectile and sabots, the materials used, the relative dimensions of certain elements... are all points that have been the subject of numerous studies and numerous innovations that allow current weapons to achieve the performances required of them.

[0027] Internal ballistics is the science that focuses on the transmission of energy from the propellant powder to the projectile. Obviously, this energy is only useful if it is transmitted to the target, that is, dissipated inside the target in order to cause significant damage. The projectile is chosen to maximize this energy transfer depending on the nature of the target and the protection applied to it. To penetrate significant armor, a long projectile of homogeneous composition offers good performance, especially if the impact speed is high. However, for softer and less armored targets, such a projectile will not be optimal, because the target will be crossed by the projectile without it transferring a significant portion of its energy to the target.

[0028] While it is clear that optimizing each of the three main parameters of internal ballistics allows for a truly remarkable level of performance to be achieved, certain physical phenomena greatly limit the level of performance accessible to this technology.

[0029] From a certain barrel length, the pressure of the propellant gases on the base of the projectile is no longer sufficient to accelerate it. Beyond this barrel length, the projectile will be slowed down by the depression forming behind it, so that increasing the barrel length only reduces the performance of the weapon. This problem has a much greater impact on small-caliber weapons than on medium and large-caliber weapons, where the optimization of certain parameters of the powder charge means that the constraints of the weapon's size (overall length, mass, inertia when aiming, etc.) will be reached before the overexpansion of the propellant gases becomes the limiting phenomenon.

[0030] The maximum pressure achievable in the barrel also quickly finds an "absolute" limit due to the performance of the materials used. At first glance, it might be tempting to consider the problem starting from the proportionality between the maximum admissible pressure in a thin-walled tube and the thickness of this tube, however this is to forget that for many weapons, the thickness of the barrel wall is of the same order of magnitude as the caliber of the ammunition and that, consequently, the hypothesis of thin walls is not satisfied.

[0031] Under these conditions, the main parameter for increasing the maximum pressure supported by the barrel is the elastic limit (and rupture) of the material used after thermal and mechanical treatment. This limit is all the lower as it is impacted by the thermal regime of the barrel during its use (repeated and close shots for machine guns and automatic cannons), but also by the limited choice of material adapted by the desired behavior in the event of obstruction (ductile behavior is preferable in order to minimize the projection of fragments in the event of destruction of the barrel).

[0032] Thus, work on the design and manufacture of "composite" barrels resulting from the assembly of several materials with different properties is relatively frequent, and, although there is no universal solution, certain combinations are quite frequent in certain uses (cobalt alloy core set with steel for machine gun barrels, etc.).

[0033] Finally, even the use of a sabot system for the propulsion of a sub-caliber projectile is limited by the maximum expansion velocity of the propellant gases inside the barrel. It is generally accepted that this maximum velocity for conventional firearms is of the order of 2300 m / s. In practice and operationally, the order of magnitude of the initial velocities reached by firearms is of the order of 1800 m / s.

[0034] To achieve higher speeds, certain technical solutions have been developed or are still being studied.

[0035] Thus, there are light gas guns using as an intermediate step in the propulsion of the projectile the compression of helium or hydrogen in a secondary chamber placed between the combustion chamber and the projectile. Similarly, there are many attempts, more or less successful, of purely mechanical magnetic, electric, electrothermal guns... While these often give promising results in terms of initial velocity of the projectile, the practical constraints of the field mean that these solutions do not find concrete and operational application. In fact, the search for new, more efficient munitions is still active.

[0036] This is the objective of this request.

[0037] To this end, the invention relates to an ammunition and weapon system, in which a projectile is pushed by a propulsion gas resulting from the combustion of a propellant charge inside a barrel closed at one end by a breech and open at its other end, characterized in that at least one part of the barrel has a conical section and in that the projectile is associated with at least one sabot which can be degraded during its movement in this part of the conical section of the barrel.

[0038] According to other characteristics of the system according to the invention, taken alone or in combination:

[0039] - the sabot is made of a material which is deposited on the barrel as it moves through it, to form a layer of thermal protection which is then removed;

[0040] - the evacuation of the protective layer of the barrel (4) is obtained:

[0041] - Either by phase change, namely liquefaction, evaporation or sublimation, of the material constituting the hoof,

[0042] Either resulting from a reaction of the material constituting the sabot with the propulsion gases resulting from the combustion of the propellant charge, or from the self-combustion of the sabot material, or from a combination of at least two of the three processes 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, centrality, camphor, phthalic ester, nitroguanidine, nitroaminoguanidine, triaminoguanidine nitrate, N - butyl - N (2 nitroxyethyl) nitramine;

[0043] - the barrel has a conical section part, followed by a rifled straight section part, the guidance of the projectile being achieved 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 latter;

[0044] - at least part of the propulsion gases generated by the combustion of the propellant charge passes through a nozzle placed in the barrel, between the breech and the projectile, and comprising a convergent, a neck and a divergent, one after the other in the direction of the open end of the barrel;

[0045] - the nozzle is formed inside a chamber removable from the barrel so as to allow the loading of the propellant charge through the rear end and the loading of the projectile through the front end of the chamber;

[0046] - the nozzle is formed inside a case forming a munition grouping the projectile and the propellant charge before firing;

[0047] - the projectile is positioned relative to the barrel before firing, by complementarity between the shape of a base of the projectile or one or more sabots and a portion of the nozzle;

[0048] - the propellant charge comprises an initiator composition, a fast-burning charge and a slow-burning charge.

[0049] The invention will be better understood on reading the following description, given solely by way of example and with reference to the appended drawings, in which:

[0050] [Fig 1] Figure 1 represents a sectional view of an embodiment of a system according to the invention with a munition in firing position;

[0051] [Fig 2] Figure 2 represents a sectional view of this system according to the invention with the ammunition fired;

[0052] [Fig 3] Figure 3 represents an enlarged-scale sectional view of a part of this system according to the invention; [Fig 4] Figure 4 represents an enlarged-scale sectional view of a part of another embodiment of a system according to the invention with a munition in the loading position;

[0053] [Fig 5] Figure 5 shows an enlarged sectional view of a portion of this further embodiment of the system according to the invention with a fired munition; and

[0054] [Fig 6] Figure 6 represents a sectional view of an embodiment of a munition of a system according to the invention.

[0055] These figures illustrate different embodiments of a system according to the invention.

[0056] This system actually uses a sub-caliber projectile guided by at least one degradable sabot inside a barrel of which at least one part has a conical section.

[0057] In these figures, the references:

[0058] I designates the breech of a cannon,

[0059] - 2 designates a combustion chamber which may be removable from the barrel so as to permit the loading of a propellant charge through the rear end and the loading of a projectile through the front end of the chamber,

[0060] - 3 denotes a nozzle with a convergent 3a, a throat 3b and a divergent 3c, one after the other in the direction of the open end of the barrel

[0061] - 4 designates the barrel with a portion of conical section 4a and a portion of straight section for example rifled 4b,

[0062] - 6 designates the mouth of the cannon,

[0063] - 7 denotes a projectile with a 7a projectile base and a 7b projectile warhead,

[0064] - 8 designates a degradable shoe,

[0065] - 9 designates a protective layer of the barrel,

[0066] 10 denotes a propellant charge with a fast-burning charge 10a, a long-burning charge Ob and an initiator composition 10c,

[0067] It designates the shock wave,

[0068] 12 designates the propellant gases, and 13 designates an ammunition with a case 13a and a primer 13b.

[0069] The caliber of the projectile is then consistent with the diameter of the barrel at its muzzle, but the internal diameter of the barrel near the chamber is significantly greater than the caliber of the projectile to accommodate the passage of the sabot.

[0070] The sabot is not so much a part in itself as a degradable seal between the projectile and the barrel. It will be progressively trimmed as the projectile passes through the conical portion of the barrel by the variation in the barrel diameter and then degraded by the temperature of the propellant gases pushing on the base of the projectile.

[0071] The aim is that in addition to performing the functions of guiding the projectile in the barrel, sealing between the barrel and the projectile, and maximizing the thrust surface of the propulsion gases during the internal ballistic phase, the transfer of the manner forming the degradable sabot on the internal face of the conical portion of the barrel creates a protective layer making it possible to limit, at least in part, the heat transfers between the propulsion gases and the barrel. This functionality is obtained by the degradation of the material acting as the degradable sabot at a temperature lower than that of the propulsion gases.

[0072] The material chosen for the degradable sabot must therefore meet a number of criteria. The density of the material used, as well as the quantity of material used, must allow the surface mass of the sabot to be lower than that of the projectile alone so that the sub-calibre of the ammunition results in improved muzzle performance. The mechanical strength of the sabot material must be sufficient to allow the transmission of the additional thrust to the projectile, but also low enough so that friction against the internal wall of the barrel causes ablative wear of the sabot. The combustion of the residues resulting from the deterioration of the sabot during firing must be as complete as possible and therefore take place while the projectile has not yet left the barrel. The combustion temperature of the sabot material must be as low as possible in order to maximise the thermal protection of the barrel.

[0073] Thus, it is possible to envisage that 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, centrality, camphor, phthalic ester, nitroguanidine, nitroaminoguanidine, triaminoguanidine nitrate, N - butyl - N (2 nitroxyethyl) nitramine. The variation in barrel diameter is continuous, progressive, but not necessarily linear. A final portion of the barrel, at the muzzle, may have the diameter necessary to bear directly on the projectile and give it a rotation necessary for its gyroscopic stabilisation.

[0074] For the designer of a firearm and its ammunition, the conical barrel technique and the sabot ammunition technique are two competing technologies belonging to the category of sub-caliber weapons and ammunition. In both cases, the aim is to resolve the dilemma of maximizing impact velocity between internal and external ballistics.

[0075] Indeed, to maximize the speed at impact on the target, for identical projectile mass, the master torque of the projectile (maximum surface area of ​​the projectile section along its main axis) is a key parameter in each of the phases of ballistics, but has an inverse influence during internal ballistics and external ballistics.

[0076] During internal ballistics, a high master torque allows for greater acceleration of the projectile due to the large surface area over which the pressure of the propellant gases is applied. However, a high master torque also considerably increases the drag force to which the projectile will be subjected during the external ballistic phase, which increases energy loss, particularly for distant targets. Conversely, a projectile with a low master torque will lose less energy during the free flight phase. However, the propulsion phase of this projectile will be negatively affected by this choice, which will limit the initial velocity of the projectile.

[0077] "Resolving" this dilemma by compromising on the projectile's master torque generally results in a muzzle 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 muzzle velocity is often necessary. In these cases, the compromise solution is no longer preferred, and the designer then turns to adopting a sub-caliber ammunition system.

[0078] Historically, the use of a variable master-torque projectile in a conical barrel is a solution that has rarely been adopted due to the complexity of implementation (production and maintenance) and the associated low performance gain. Indeed, the need to gradually vary the internal diameter of the tube to move from a high master-torque in the initial phase of the internal ballistics to a low master-torque at the muzzle of the barrel implies that the solution only has an effect at the beginning of the thrust phase. Thus the performance gain is relatively limited and applications where the initial velocity of the projectile exceeds 1500 m / s are rare. Nevertheless, it should be noted that this solution also offers the advantage of allowing the firing of gyro-stabilized munitions without tails.

[0079] The other major family of ammunition sub-caliber solutions is the use of a so-called "sabot" ammunition where the low-torque projectile is clamped by a sabot that seals with the barrel during the internal ballistic phase. The main advantage of this solution lies in the use of a high torque along the entire length of the barrel, which maximizes the thrust on the projectile until it leaves the barrel. However, this process also affects the propulsion efficiency, because part of the energy is used to accelerate the sabot, the mass of which can be around 30% of the mass of the projectile. In addition, 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 that will only be damped by the presence of a stabilizing fin moving the center of drag to the rear of the center of gravity of the projectile.Therefore, sabot ammunition is most often used in conjunction with a smoothbore gun, the projectile being mainly stabilized by a tail having a certain incidence relative to the axis of the projectile in order to give it additional gyroscopic stability via the rotation of the projectile in the initial phase of external ballistics (transient ballistics).

[0080] In practice, two sabot technologies are used: a monolithic sabot pushing the projectile from the rear and positioning the projectile via lateral petals that will spread apart as it leaves the barrel. These munitions are called SLAP for "Saboted Light Armor Penetrator". The other solution consists of several sabots in the form of a portion of a hollow revolution part that grips the projectile laterally. The sabots separate from the projectile as it leaves the barrel under the effect of aerodynamic forces and inertia. The resulting munition is designated APDS for "Armor Piercing Discarding Sabot" when the projectile is without a stabilizing fin, and APFSDS for "Armor Piercing Fin-Stabilized Discarding Sabot" when the stabilization of the projectile is achieved by a rear fin.

[0081] A solution like that proposed by the invention consisting of a mixture between these two solutions (conical barrel and saboted projectile) is not one of the likely options retained when designing a new weapon due to the accumulation of disadvantages (reduction of the thrust surface as the projectile advances in the barrel and increase in the mass propelled by a sabot mass) without there being any accumulation of advantages. Thus, no obvious performance gain is expected by the designer while the complexity of the development is glaring. The evolution of needs in the field of firearms, in particular the constraints linked to the penetration of armor, pushes designers of weapons and ammunition into a race for performance resulting in the adoption of high initial velocities.However, to meet customer expectations, the current trend is to increase the pressure in the barrels of small and medium-caliber weapons. However, certain limitations are clearly reached with regard to the choice of materials and their resistance. This is all the more striking in the case where the weapon must be able to fire at a high rate of fire over a prolonged period. In this case, it is necessary to take into account the reduction in the resistance of the material used for the barrel linked to the rise in temperature. This phenomenon implies an upper limit to the service pressure of ammunition which is currently around 600 MPa for steel barrels. The use of such a high service pressure implies severe limitations with regard to the service life of the barrel as well as restrictions on the firing regimes for weapons likely to fire at a high rate of fire.

[0082] In order to allow a significant gain in performance without being penalized by the capping of the maximum pressure admissible by the barrel, the question of the use of sub-calibre ammunition must be reconsidered.

[0083] The practicality of gyroscopic stabilization argues in favor of using the conical barrel method combined with a deformable projectile. This is all the more obvious since this method is, at first glance, more suitable for mass production compared to the production of a projectile and sabot assembly. Usually, this solution is not retained due to the fact that a deformable projectile does not make a good penetrator. It is therefore necessary to resort to a projectile in two parts: a deformable body and a hard core which will serve as a penetrator. It is generally this constraint which pushes the weapons designer to turn to the use of a sabot and therefore to abandon the conical barrel solution for the adoption of an APDS projectile.

[0084] However, by continuing the study of a conical barrel combined with the use of APDS ammunition, a weapon designer realizes that the accumulation of expected defects is presented in the following form: the conicity of the barrel reduces the thrust surface of the combustion gases on the base of the projectile, the adoption of a sabot reduces the thrust efficiency by the addition of a propelled mass whose energy 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 its mass can decrease as it advances in the barrel from the moment when this sabot is made of a material capable of degrading / eroding on the walls of the barrel. If we consider erosion of the degradable sabot linked to the conicity of the barrel, we note that the mass of the accelerated assembly (projectile and sabot) decreases as the projectile advances and gains speed.Thus, 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 this configuration, the penalty linked to the use of a sabot is reduced even if it is replaced by that linked to the reduction of the gas thrust section on the projectile and sabot assembly. Consequently, the level of performance achievable via this method is, at a minimum, comparable to the level of performance achievable by the conical barrels already known.

[0085] The material that will be detached from the sabot by its abrasion inside the conical barrel then forms a layer on the inner wall of the barrel. This layer must be evacuated, preferably between each shot, 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 as a negative point for the maintenance of a weapon, in particular when the weapon operates repeatedly via an automation using a gas borrowed from the barrel. Thus, it becomes necessary to manage the evacuation of the sabot in a form other than a support for the projectile.

[0086] One solution is to choose the material constituting the sabot as previously indicated, giving it the properties necessary for its evacuation in the form of gas at the same time as the propellant gases resulting from the combustion of the propellant charge. This implies that the material used for the degradable sabot must have a vaporization or sublimation temperature lower than the temperature of the propellant gases during firing. Many polymers fall into this category; waxes are also fairly good candidates.

[0087] Another possibility is to make the degradable sabot material interact with the propellant gases resulting 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 high enough that the excess oxygen can react with the material composing the degradable sabot to form a gas that mixes with the propellant gases and will therefore be evacuated like the latter. Materials with properties conducive to this type of strategy are polymers composed mainly of carbon chains, graphite, etc. Materials that are difficult to oxidize or whose oxidation residues 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, to create the degradable sabot. In this case, the advantage is that the combustion of the material serving as the degradable sabot, and then as the protective layer, is ensured by exposure to the temperature and pressure of the propellant gases. Another advantage is that the energy contained in the degradable sabot is added to that of the propellant charge in the form of an increase in the quantity of propellant gas in the barrel behind the projectile as well as an increase in the temperature of the propellant gases in the barrel.

[0088] In fact, mechanical constraints (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. Consequently, 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 the composite solutions, compositions close to those used in solid rocket motors, combining an oxidizer and a reducer held together by a resin, form a family of promising solutions.

[0089] It is noteworthy that leaving a layer of material inside the barrel when the projectile passes through can also have a secondary function of insulation (even temporary) between the inner wall of the barrel and the hot propulsion gases. Indeed, the fact that the residual layer, called the protective layer, after the sabot has passed through is only able to withstand a moderate temperature before sublimating and, possibly, reacting chemically, creates a form of temporary barrier between the propulsion gases and the inner surface of the barrel. Consequently, the inner wall of the barrel is not subjected to a temperature higher than the sublimation temperature of the degradable sabot material until it has been completely detached from the wall.It is possible to maximize this effect by selecting the degradable sabot material in relation to its sublimation temperature, or by integrating reactive additives playing a moderating role in the propellants (graphite, potassium, centrality, 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, etc.

[0090] It is important to note that the insulation effect of the internal wall of the barrel is maximal for a short barrel with a rapid reduction of the internal section. This geometry is generally associated with a compact and lightweight weapon, which is a common feature of many weapons firing in more or less long bursts at relatively high rates. These weapons generally derive their effectiveness from a saturation effect of the targeted area and not from the individual power of each projectile launched. In this case, the use of a combination of a barrel with a high taper and a degradable sabot ammunition allows a certain reduction in the thermal stress of the barrel with equivalent performance.Consequently, the weapon designer will be able to afford some reduction in barrel wall thickness to reduce the weapon's mass, the removal of a quick barrel replacement system (usually found on infantry machine guns), or an increase in the acceptable firing rate if the weapon's mass is not an issue. Conversely, weapons that combine high power with accuracy are generally already equipped with long, large-diameter barrels. Thus, there is no particular penalty for these weapons due to the adoption of degradable sabot ammunition combined with a barrel with moderate taper.

[0091] In any case, the evacuation of the protective layer of the barrel is obtained, for example:

[0092] - either by phase change, namely liquefaction, evaporation or sublimation, of the material constituting the sabot, or which may result from a reaction of the material constituting the sabot with the propulsion gases resulting from the combustion of the propellant charge, or from the self-combustion of the material of the sabot, or from a combination of at least two of the three processes described.

[0093] Another constraint to consider is the need to keep the projectile coaxial with the barrel while it is accelerated by the sabot in the conical section of the barrel.

[0094] The concentricity of the projectile in the barrel does not pose any particular problem, because the breakdown of contact on one side of the barrel automatically causes an imbalance of radial forces from the barrel onto the degradable sabot, which will be redirected to an equilibrium position in the center of the barrel. In this case, it is the conicity of the barrel that ensures the permanent recentering of the projectile in the barrel.

[0095] The coaxiality of the projectile in the barrel is at first sight more problematic. Two cases are to be considered. In the case of long guidance of the projectile in the barrel, that is to say a contact length between the degradable sabot and the barrel significantly greater than the external diameter of the degradable sabot, it is preferable that the front and rear faces are significantly stronger than the core of the sabot. Thus, 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 ensures the coaxiality of the projectile with respect to the barrel.

[0096] However, it is not always possible to ensure long guidance between the degradable sabot and the conical barrel. In this case, the condition of coaxiality of the projectile in the barrel lies in the positioning behind the center of gravity of the projectile and degradable sabot assembly with respect to the contact zone between the sabot and the barrel. Indeed, if this condition is met, when the projectile is no longer coaxial with the barrel, the center of gravity of the projectile and degradable sabot assembly shifts towards the "advanced" side due to the rotation of the projectile and degradable sabot assembly around the center of guidance. The distribution of the mass of the projectile and degradable sabot assembly on the thrust surface of the propulsion gases is modified with a greater mass on the "advanced" side and a lesser mass on the "late" side.Since the thrust pressure of the propulsion gases is relatively uniform, the acceleration on the "lagging" side will be greater than that on the "leading" side, which will result in bringing the projectile into a coaxial position with the gun.

[0097] It is interesting to note at this point that the appropriate shape for the base of the degradable sabot to meet this last stability condition is quite close to a cone pointing towards the breech of the weapon. This shape makes it possible to satisfy the coaxiality condition by short guidance when the main torque of the barrel is high (close to the breech) and to gradually move to long guidance as the diameter of the degradable sabot decreases due to the conicity of the barrel.

[0098] It will be noted that this shape can be complementary to a nozzle shape as described later. Two obvious advantages can be drawn from this configuration.

[0099] The first advantage is in the order of the rigidity of the ammunition for the guidance and chambering manipulations of the ammunition in the barrel. Indeed, it is thus possible to reduce the transmission by the degradable sabot of the lateral forces on the tip of the projectile during these operations by working the shape of the base of the projectile so that there is contact between the base of the projectile and the neck and / or the divergent part of the nozzle of the case. The second advantage of this configuration relates to the industrialization of the ammunition. Indeed, in a configuration where the base of the projectile is in contact with the neck and / or the divergent part 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 imprint positioning the projectile and being closed by the case.

[0100] Another point of the system according to the invention concerns 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. This separation is achieved by means of a nozzle allowing the passage of gases at supersonic speed inside the barrel.

[0101] To do this, several architectures are possible depending on the nature of the desired weapon and the accepted drawbacks:

[0102] If the weapon in question is a muzzle-loading weapon, the nozzle may be permanently fixed and formed directly by the barrel. In this case, the propellant charge may be introduced through the muzzle if the propellant charge is in the form of a powder fine enough to be introduced into the chamber through the nozzle and the neck. Preferably, the propellant charge is introduced into the chamber through the breech in the form of pellets or a blank cartridge. The projectile is always introduced through the muzzle. All types of conventional or sub-caliber projectiles are compatible with these configurations.

[0103] If the weapon is necessarily exclusively breech-fed, 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 case without any particular modification to be made to the weapon. This last configuration is preferred because of its practicality in terms of loading operations, evacuation of firing waste, unloading of the weapon or cleaning of the system.

[0104] Thus the nozzle can be formed inside a chamber removable from the barrel so as to allow the loading of the propellant charge by the rear end and the loading of the projectile by the front end of the chamber or this nozzle can be formed inside a case forming a munition grouping the projectile and the propellant charge before firing. In addition, the projectile can be placed inside the munition case by complementarity between the shape of a base of the projectile or of one or more sabots and of a portion of the nozzle while the munition is assembled.

[0105] The modeling of the internal ballistics of firearms is well known and is based on a set of equations used to determine the evolution of certain parameters in order to deduce the evolution of the velocity and position of the projectile during firing. One of these equations represents the energy balance inside the barrel and highlights the partial transfer of the energy released by the propellant charge into 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 propellant gases (which acts as a form of potential energy reserve allowing the continuation of the propulsion of the projectile in the barrel, while the combustion of the propellant charge is complete), and the setting in motion of the propellant gases (energy which is lost).

[0106] If we stick to this modeling, an artifice inside the barrel resulting in an increase in the velocity of the propulsion gases is necessarily detrimental to the internal ballistics since it increases the kinetic energy of these same propulsion gases and therefore reduces the energy available to the projectile. Consequently, the introduction of a reduced passage section of the propulsion gases, compared to the passage section of the projectile in the barrel, at the exit of the chamber is considered a design error with regard to the creation of a high velocity ammunition.

[0107] However, this would also be forgetting that the amount of energy available is actually limited only by the amount of propellant used (and therefore by the capacity of the chamber). Another more limiting factor for the performance of a barrel-ammunition pair is none other than the maximum pressure that the barrel can withstand. Thus, a loss of efficiency in the priming and early propulsion phase of the projectile is not necessarily a handicap for the performance of the barrel-ammunition pair if another phenomenon allows the limitations of maximum pressure that the barrel can withstand to be overcome.

[0108] In the barrel, the static pressure exerted on the internal walls of the barrel is related to the static pressure at the breech as well as to the velocity of the propellant gases at the location of the barrel in question. The faster the propellant gases, the more the static pressure exerted on the barrel walls decreases. In a conventional barrel, this results in a decrease in the maximum pressure reached as one moves towards the muzzle. This is explained by the LAGRANGE hypothesis which states that the variation in gas velocity is linear between the breech and the base of the projectile.This phenomenon is all the more marked since, very often, the combustion of the propellant powder is complete while the projectile has not yet exceeded half the length of the barrel (in particular for long-barreled shoulder weapons), which implies that the peak of total available pressure (static pressure at the breech) is already exceeded while the projectile is still in the barrel. For weapons adapted to firing rapid projectiles, the barrel is formed of a tube whose wall thickness is often quite close to, or even greater than, the diameter of the projectile. This implies that the internal stress that the barrel can withstand during a shot is less and less correlated with the increase in the external diameter of the tube (hypothesis of thin hollow cylinders), but that the limiting factor becomes the limit to rupture of the material used for the barrel bore.In fact, the limit to the maximum operating pressure of ammunition is directly linked to innovation in the field of high-toughness materials, including at high temperatures, and whose failure mode is compatible with the safety of the weapon. Indeed, in the event of an obstruction, a barrel that bursts (opens along a crack without the creation and dispersion of fragments) is preferable to bursting behavior (brittle fracture with projection of fragments).

[0109] Therefore, there is a major interest for a weapon designer to seek to reduce the static pressure applied to the internal walls of the barrel while maximizing the pressure experienced by the base of the projectile to maintain, or increase, the performance of the weapon - ammunition pair. To do this, modifying the distribution of the velocity of the propulsion gases between the breech and the base of the projectile is an interesting option which has unfortunately not been studied.

[0110] 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 device inside the barrel which will have the function of increasing the velocity of the propulsion gases and therefore reducing the pressure on the internal walls of the barrel. Since the modification of the flow of propulsion gases inside the barrel takes place mainly downstream of the device, it is necessary that the device accelerating the propulsion gases be placed as close as possible to the breech so that the largest part of the barrel benefits from the advantages granted.

[0111] The device that allows the transition between a high-pressure reservoir on the breech side (called the chamber) and the barrel, where the pressure is lower and the speed of the propellant gases is particularly high, is nothing other than a nozzle. This is characterized by a throat, the narrowest passage through which the propellant gases pass, a convergent part accelerating the propellant gases to sonic speed and a divergent part bringing the propellant gases to supersonic speed.

[0112] In the initial state, the entire propellant charge is in the chamber, which is closed by the nozzle neck and the projectile. When the ammunition is fired, a priming phase begins, which can be modeled in the same way as the internal ballistics of a traditional firearm of the same type. However, it is necessary to take into account the pressure drop when passing through the nozzle. The end of the priming phase is characterized by a speed of passage of the propellant gases through the neck at the speed of sound in this same gas. At this moment, a shock wave is created at the neck and decouples the chamber, where a high static pressure prevails, forcing the combustion of the still unburned powder, from the barrel, in which the nozzle ejects the product of the combustion of the propellant charge at a supersonic speed and a lower static pressure.

[0113] These propellant gases are compressed again at the base of the projectile, which thus continues its propulsion phase in the barrel. The pressure to which the base of the projectile is subjected is linked to two components: the static pressure at the nozzle outlet and a dynamic component linked to the difference between the ejection speed of the propellant gases at the nozzle and the speed of the projectile in the barrel. Thus the pressure applied to the internal walls of the barrel is significantly lower than the pressure exerted in the chamber, with a distribution passing through a minimum at the nozzle outlet and a progressive recompression towards the pressure at the base of the projectile.

[0114] The projectile can then be placed inside the ammunition case by complementarity between the shape of a base of the projectile or one or more sabots and a portion of the nozzle as long as the ammunition is assembled.

[0115] The construction and operating constraints 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 costly in terms of performance, to reinforce the chamber than the entire barrel. The reduction in static pressure inside the barrel is also accompanied by a reduction in the temperature of the gases in the barrel.

[0116] To facilitate the transition to supersonic speed of the combustion gases at the nozzle throat, it is preferable to use a method of increasing the projectile speed by a method of sub-calibrating the projectile relative to the barrel. Since the objective is to obtain decoupling of the chamber as quickly as possible, the sabot technique is as well suited as the technique of the deformable projectile in a conical barrel. It should be noted, however, that the technique of the degradable sabot projectile accelerated by a conical barrel offers certain synergies if it is combined with the adoption of a nozzle in the barrel.

[0117] Of course, other embodiments can be considered.

Claims

DEMANDS 1 Munition and weapon system, in which a projectile (7) is propelled by a propellant gas from the combustion of a propellant charge (10) inside a barrel (4) closed at one end by a breech (1) and open at its other end, characterized in that at least a part of the barrel (4) has a conical section (4a) and in that the projectile (7) is associated with at least one sabot (8) which is degradable during its movement in this part of the conical section of the barrel. 2 System according to claim 1, characterized in that the shoe (8) is made of a material which is deposited on the barrel (4) as it moves in it, to form a thermal protection layer (9) of the latter which is then evacuated.

3. System according to claim 2, characterized in that the evacuation of the protective layer of the barrel (4) is achieved: - either by phase change, namely liquefaction, evaporation or sublimation, of the material constituting the shoe, or resulting from a reaction of the material constituting the shoe with the propulsion gases from the combustion of the propellant charge, or from the self-combustion of the material of the shoe, or from a combination of at least two of the three processes described. 4 System according to any one of claims 1 to 3, characterized in that the shoe 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, centrality, camphor, phthalic ester, nitroguanidine, nitroaminoguanidine, triaminoguanidine nitrate, N-butyl-N(2-nitroxyethyl)nitramine.

5. A system according to any one of claims 1 to 4, characterized in that the barrel (4) comprises a portion with a conical cross-section (4a), followed by a portion with a cross-section rifled right (4b), the guidance of the projectile (7) being achieved by the sabot (8) in the conical section of the barrel and by direct contact between the projectile and the barrel in the right section thereof. 6 System according to any one of claims 1 to 5, characterized in that at least a part of the propulsion gases generated by the combustion of the propellant charge (10) passes through a nozzle (3) placed in the barrel (4), between the breech (1) and the projectile (7), and comprising a convergent (3a), a throat (3b) and a divergent (3c), one after the other in the direction of the open end of the barrel. 7 System according to claim 6, characterized in that the nozzle (3) is formed inside a removable chamber (2) relative to the barrel (4) so ​​as to allow the loading of the propellant charge from the rear end and the loading of the projectile from the front end of the chamber. 8 System according to claim 6, characterized in that the nozzle (3) is formed inside a case (13a) forming a munition (13) grouping the projectile and the propellant charge before firing. 9 System according to claim 8, characterized in that the projectile (7) is positioned relative to the barrel (4) before firing, by complementarity between the shape of a base (7a) of the projectile or of one or more sabots (8) and a portion of the nozzle (3). 10 System according to any one of the preceding claims, characterized in that the propellant charge comprises an initiating composition (10c), a fast-burning charge (10a) and a slow-burning charge (10b).

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