FR3135778A1 - AMMUNITION AND WEAPON SYSTEM - Google Patents

Abstract

TITLE: AMMUNITION AND WEAPON SYSTEM This ammunition and weapon system, in which a projectile (7) is propelled by a propellant gas resulting 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, is characterized in that at least 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 neck (3b) and a divergent (3c), one at the following the other towards the open end of the barrel. Figure for abstract: Figure 3

Description

AMMUNITION AND WEAPON SYSTEM

The present invention relates to an ammunition and weapon system.

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.

Firearms include all weapons that use an exothermic chemical reaction in their operation. By semantic shift, this term is often associated with tube weapons whose principle is based on the launch of a projectile inside a barrel.

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

This phase of ballistics is called interior ballistics.

Over the years, firearms have undergone numerous refinements which have notably seen the introduction of the cartridge case (sometimes also called a case) which allows the components necessary for firing (primer, propellant powder, projectile) to be brought together in a single block. called ammunition.

By construction, the cannons have a geometry quite close to a hollow cylinder whose internal section is relatively constant over the trajectory of the projectile (except for conical cannons).

When the designer of the weapon and its ammunition wishes to maximize the initial speed of the projectile, there is no element likely to restrict the flow of propulsion gases behind the projectile.

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 precedence over muzzle-loading weapons even if certain uses are still common (light mortars).

An exception to this rule is when a relatively low initial projectile velocity is desired (primarily grenade launchers). In this case, the socket draws two chambers, the high pressure chamber, which contains the propellant charge, and in which the combustion takes place, and a low pressure chamber in which the expansion of the propulsion gases which push on the base of the projectile. 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.

Maximizing the muzzle velocity of a projectile is a constant concern of weapons designers, as it grants a number of advantages in subsequent phases of ballistics. During external ballistics and for the same projectile, this makes it possible to obtain a more “straight” trajectory which significantly reduces the sensitivity to wind, the time to impact on the target and the aiming corrections to be taken into account depending on distance, inclination of the shot…

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

Thus research aimed at firing faster and faster projectiles has always been active and has provided a certain number of technical solutions in the field of firearms.

Thus, at the level of weapons and ammunition, three main avenues are often explored:

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

The second option is the maximization of the pressure of the propulsion 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 construct cannons that cap the maximum internal pressure. This is all the more problematic as the thermal stresses involved in each shot deteriorate the resistance of the barrel.

When the two previous avenues are already the subject of a certain optimization, the designer of the ammunition may be obliged to resort to the adoption of a lightweight projectile called “under-calibrated”. In this case, the projectile which will impact the target is very elongated and has a diameter significantly less than the internal diameter of the gun which is used in order to limit its drag during the external ballistic phase and concentrate the energy on impact. to maximize terminal effects. However, during the projectile propulsion phase, 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 interior ballistics phase.

Two solutions are relatively known to achieve these results:

1. The use of a deformable projectile inside a conical barrel having a significantly greater internal diameter on the chamber side than on the muzzle side (like the German 28-20mm cannon). In this case, the seal 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 as it travels the length of the barrel.
2. The use of an intermediate sabot between the projectile and the barrel during the interior ballistics phase and separating from the projectile when exiting the barrel. The shoe is made of a low density material such as aluminum or certain polymers. It can be in one piece pressing on the rear face of the projectile (SLAP ammunition) or in several parts united around the projectile by belts and releasing it by spreading radially (APFSDS ammunition).

Although it is important to minimize friction between the projectile and the barrel, it is nevertheless necessary to guarantee a good seal so as to avoid the passage of part of the propulsion gases in front of the projectile inside the barrel. . When this is the case, the initial speed of the projectile is greatly impacted as well as barrel wear is accelerated. Historically, the sealing function was fulfilled by a wad placed behind the projectile (at the time of paper cartridges). As the means of production improved and the geometry of cannons and projectiles became better controlled, this function was fulfilled by the tightening and deformation of the projectile (made of lead then lined with copper) in the cannon. 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”.

More anecdotally, some shooters do not hesitate to use specific greases on small caliber projectiles. For shooting 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 above all in creating a seal for the powder against external humidity when storing a stocked weapon. It is however admitted that the protection sought with these devices relates to the interaction between the projectile and the barrel and has only a negligible effect on the aspects linked to the thermal of the barrel.

Each of these themes is well known to weapons and ammunition designers so much so that it is sometimes possible to find the conceptual signature of certain solutions currently in use in weapons at the cutting edge of technology in patents dating from the 19th century. . For example, it is difficult to ignore the resemblance between a current 120 mm APFSDS ammunition from the LECLERC tank and the ammunition described in US patent 487,125 dating from 1892. Both feature semi-combustible cases with a metal base to facilitate the sealing of the chamber at the level of 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... However, there is no doubt that numerous Advances have been made between the publication of this patent and modern munitions. 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 numerous studies and numerous innovations which allow current weapons to achieve the performance required of them.

Internal ballistics is the science concerned with 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 to say dissipated inside the target in order to create significant damage. The projectile is chosen so as to maximize this energy transfer depending on the nature of the target and the protection applied to it. To pierce heavy armor, a long projectile of homogeneous composition offers good performance, particularly 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 part of its energy 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 completely remarkable level of performance, certain physical phenomena greatly limit the level of performance accessible to this technology.

From a certain barrel length, the pressure of the propulsion gases on the base of the projectile is no longer sufficient to accelerate the latter. 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 impacts small caliber weapons much more than medium and large caliber weapons where the optimization of certain powder charge parameters means that the bulk constraints of the weapon (overall length, mass, pointing inertia …) will be reached before the overexpansion of the propulsion gases is the limiting phenomenon.

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 The thickness of the barrel wall is of the same order of magnitude as the caliber of the ammunition and therefore the thin wall assumption is not satisfied.

Under these conditions, the main parameter allowing the maximum pressure supported by the barrel to be increased is the elastic (and breaking) limit 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 gun during its use (repeated and close shots for machine guns and automatic cannons), but also by the limited choice of material adapted by the behavior desired 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).

Thus, work concerning 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 common 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 speed of expansion of the propulsion gases inside the barrel. It is generally accepted that this maximum speed for conventional firearms is around 2300 m/s. In practice and operationally, the order of magnitude of the initial speeds reached by firearms is of the order of 1800 m/s.

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

Thus, there are light gas cannons using as an intermediate step in propelling the projectile the compression of helium or hydrogen in a secondary chamber placed between the combustion chamber and the projectile. Likewise, there have been numerous attempts, more or less successful, at purely mechanical magnetic, electric, electrothermal cannons... If these often give promising results in terms of initial speed of the projectile, the practical constraints of the field mean that these solutions do not find concrete and operational application. In fact, the quest for new, more efficient ammunition is still active.

This is the objective of this request.

For this purpose the invention relates to an ammunition and weapon system, in which a projectile is pushed by a propellant 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 part of the propulsion gases generated by the combustion of the propellant charge pass through a nozzle placed in the barrel, between the breech and the projectile, and comprising a convergent, a neck and a diverging, one after the other towards the open end of the barrel.

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

- the nozzle is formed inside a removable chamber relative to 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;

- the nozzle is formed inside a case forming an ammunition grouping the projectile and the propellant charge before firing;

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

- the propellant charge comprises an initiator composition, a rapid combustion charge and a slow combustion charge;

- at least one part of the barrel has a conical section and in that the projectile is associated with at least one degradable shoe when it moves in this conical section part of the barrel;

- the shoe is made of a material depositing on the barrel as it moves through it, to form a thermal protection layer for it which is then evacuated;

- the evacuation of the protective layer of the barrel is obtained:

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

- 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 , centralite, camphor, phthalate esther, nitroguanidine, nitroaminoguanidine, triaminoguanidine nitrate, N – butyl – N (2 nitroxyethyl) nitramine;

- the barrel comprises a part of conical section, followed by a part of rifled straight section, the guidance of the projectile being carried out 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 this one.

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

• There represents a sectional view of an embodiment of a system according to the invention with ammunition in the firing position;
• There represents a sectional view of this system according to the invention with the ammunition fired;
• There represents a sectional view on an enlarged scale of a part of this system according to the invention;
• There represents an enlarged sectional view of a part of another embodiment of a system according to the invention with ammunition in the loading position;
• There represents a sectional view on an enlarged scale of a part of this other embodiment of the system according to the invention with fired ammunition; And
• There represents a sectional view of an embodiment of a munition of a system according to the invention.

We have in fact illustrated in these figures different embodiments of a system according to the invention.

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

In these figures, the references:

• 1 designates the breech of a cannon,
• 2 designates a combustion chamber which can be removable relative to the barrel so as to allow the loading of a propellant charge through the rear end and the loading of a projectile through the front end of the chamber,
• 3 designates a nozzle with a convergent 3a, a neck 3b and a divergent 3c, one after the other towards the open end of the barrel,
• 4 designates the barrel with a portion of conical section 4a and a portion of straight section, for example rifled, 4b,
• 6 designates the muzzle of the cannon,
• 7 designates a projectile with a projectile base 7a and a projectile warhead 7b,
• 8 designates a degradable clog,
• 9 designates a protective layer of the barrel,
• 10 designates a propellant charge with a rapid combustion charge 10a, a long combustion charge 10b and an initiator composition 10c,
• 11 designates the shock wave,
• 12 designates propulsion gases, and
• 13 designates an ammunition with a 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 internal diameter of the barrel near the chamber is significantly greater than the caliber of the projectile to accommodate the passage of the sabot.

The sabot is not so much a part in itself as a degradable joint 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 diameter of the barrel then degraded by the temperature of the propulsion gases pushing on the base of the projectile.

The goal is that in addition to carrying out 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 ballistics phase, the transfer in the manner forming the degradable sabot on the internal face of the conical portion of the barrel produces a protective layer making it possible to limit, at least in part, the thermal transfers between the propulsion gases and the barrel. This functionality is obtained by the degradation of the material acting as a degradable shoe at a temperature lower than that of the propulsion gases.

The material chosen for the degradable clog must therefore meet a certain 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 undercalibration of the ammunition results in an improvement in performance. mouth. The mechanical strength of the sabot material must be sufficient to allow the transmission of the additional thrust to the projectile, but also sufficiently low 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 maximize the thermal protection of the barrel.

Thus we can envisage 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, centralite, camphor, phthalate esther, 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, can have the diameter necessary to rest directly on the projectile and give it a rotation necessary for its gyroscopic stabilization.

For the designer of a firearm and its ammunition, the conical barrel technique as well as that of sabotaged ammunition are two competing technologies belonging to the category of undercalibrated weapons and ammunition. In both cases, it is a question of resolving the dilemma of maximizing the impact speed between interior ballistics and exterior ballistics.

Indeed, to maximize the speed upon impact on the target, for the same mass of projectiles, 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 the ballistic, but has an inverse influence during interior ballistics and exterior ballistics.

During interior ballistics, a strong master torque allows greater acceleration of the projectile due to the large surface area on which the pressure of the propulsion gases is applied. However, a strong master torque also considerably increases the drag force to which the projectile will be subjected during the external ballistic phase, which increases the 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 speed of the projectile.

The “resolution” of this dilemma by a compromise on the master torque of the projectile generally results in an initial velocity of less than 1000 m/s for an acceptable barrel length 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 favored, and the designer then turns to the adoption of an under-calibrated ammunition system.

Historically, the use of a projectile with variable master torque in a conical barrel is a solution which has rarely been adopted due to the complexity of implementation (production and maintenance) and the low associated performance gain. Indeed, the need to gradually vary the internal diameter of the tube to go from a high master torque in the initial phase of internal ballistics to a low master torque at the muzzle of the gun implies that the solution does not have to effect only in the beginning of the pushing phase. Thus the performance gain is relatively limited and there are few applications where the initial speed of the projectile exceeds 1500 m/s. However, it should be noted that this solution also offers the advantage of allowing the firing of gyro-stabilized munitions without tails.

The other large family of solutions for sub-calibration of the ammunition is the use of a so-called “sabot” munition where the projectile with low master torque is enclosed by a sabot providing sealing with the barrel during the phase. interior ballistics. The main advantage of this solution lies in the use of a significant master torque over the entire length of the barrel, which maximizes the thrust on the projectile until it exits the barrel. However, this process also affects the efficiency of the propulsion, 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. Additionally, 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 damped by the presence of a stabilizing tail moving the center of drag to the rear of the center of gravity of the projectile. Consequently, sabot ammunition is most often used in conjunction with a smoothbore cannon, the projectile being mainly stabilized by a tail having a certain incidence in relation to the axis of the projectile in order to grant it additional gyroscopic stability via the rotation of the projectile in the initial phase of external ballistics (transient ballistics).

In fact, two sabot technologies are implemented: a monolithic sabot pushing the projectile from the rear and positioning the projectile via lateral petals which will move apart when exiting the barrel. These munitions are called SLAP for “Saboted Light Armor Penetrator”. The other solution consists of several sabots taking the form of a portion of a hollow piece of revolution which surrounds the projectile laterally. The sabots separate from the projectile upon exiting the barrel under the effect of aerodynamic forces and inertia. The resulting ammunition is designated APDS for “Armor Piercing Discarding Sabot” when the projectile is without a stabilizing tail, and APFSDS for “Armor Piercing Fin-Stabilized Discarding Sabot” when the stabilization of the projectile is obtained by a rear tail.

A solution like that proposed by the invention consisting of a mixture between these two solutions (conical barrel and sabotaged projectile) is not one of the options likely to be retained during the design of 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 the designers of weapons and ammunition into a race for performance resulting in the adoption of high initial velocities . However, to meet customer expectations, the trend is currently to increase the pressure in the barrels of small and medium caliber weapons. However, certain limitations are clearly reached regarding the choice of materials and their resistances. This 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 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 thereof. This phenomenon implies an upper limit to the operating pressure of an ammunition which is currently of the order of 600 MPa for steel barrels. The use of such a high operating pressure implies severe limitations on barrel life as well as restrictions on firing regimes for weapons likely to fire at high rates.

In order to allow a significant gain in performance without being penalized by the capping of the maximum pressure admissible by the guns, the question of the use of under-calibrated ammunition must be reconsidered.

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

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 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 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 barrel walls.

If we consider erosion of the degradable sabot linked to the taper of the barrel, we notice 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 degradable sabot mass 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 in 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 already known conical barrels.

The material which will be detached from the sabot by its abrasion inside the conical barrel then forms a layer on the internal 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, pronounced fouling of the barrel is considered a negative point for the maintenance of a weapon, in particular when the weapon operates repeatedly via an automation using gas borrowing in the barrel. Thus, it becomes necessary to manage the evacuation of the sabot in a form other than a support for the projectile.

One solution is to choose the material constituting the sabot as indicated previously, giving it the properties necessary for its evacuation in the form of gas at the same time as the propulsion 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 propulsion gases during firing. A lot of polymers fall into this category, waxes are also quite good candidates.

Another possibility is to make the material of the degradable sabot interact with the propulsion 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 large enough for the excess oxygen to react with the material making up the degradable sabot to form a gas which mixes with the propulsion 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 oxidise or whose oxidation residues are not in the gaseous state at the temperature and pressure present. in the barrel are not good candidates for making a degradable sabot.

Finally, it is possible to use a material containing both the oxidant and the reducer, that is to say a propellant, to create the degradable shoe. In this case, the advantage is that the combustion of the material serving as a degradable shoe, then as a protective layer, is ensured by exposure to the temperature and pressure of the propulsion gases. Another advantage is that the energy contained in the degradable sabot adds to that 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 temperature propulsion gases in the barrel.

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 material of the sabot, 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, a perfectly indicated solution for the production of a degradable clog. Among the composite solutions, compositions close to those used in powder rocket engines, combining an oxidant 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 function of insulation (even temporary) between the internal wall of the barrel and the hot propulsion gases. Indeed, the fact that the residual layer, called the protective layer, after the passage of the hoof is only capable of withstanding a moderate temperature before sublimating and, possibly, reacting chemically, creates a form of temporary barrier between the propulsion gas and the internal surface of the barrel. Consequently, the internal 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 material of the degradable sabot in relation to its sublimation temperature, or by integrating reactive additives playing a moderating role in the propellants (graphite, potassium, centralite, camphor, phthalic esther, etc.), or by using at least one other stabilizer and flame temperature reducer such as nitroguanidine, nitroaminoguanidine, triaminoguanidine nitrate or even N – butyl – N (2 nitroxyethyl) nitramine….

It is important to note that the insulation effect of the internal wall of the barrel is maximum for a short barrel with a rapid reduction in the internal section. This geometry is generally associated with a compact and lightweight weapon, which is a trait common to many weapons firing in bursts of varying length at relatively high rates. These weapons generally derive their effectiveness from a saturation effect on the targeted area and not from the individual power of each projectile launched. In this case, the use of a combination between a barrel with a strong conicity and an ammunition with a degradable sabot allows a certain reduction in the thermal stress of the barrel with equivalent performance. Consequently, the weapon designer will be able to afford a certain 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 (generally present on infantry machine guns) or an increase in the acceptable firing rate if the mass of the weapon is not a problem. Conversely, weapons combining high power of each shot and precision are generally already equipped with long and large diameter barrels. Thus there is no particular penalty for these weapons due to the adoption of a degradable sabot ammunition associated with a barrel with moderate conicity.

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

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

Another constraint to take into account 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.

The concentricity of the projectile in the barrel does not pose a particular problem, because breaking the contact on one side of the barrel automatically causes an imbalance in the radial forces of the barrel on the degradable sabot which will be redirected towards an equilibrium position in the center of the barrel. canon. In this case, it is the taper of the barrel which ensures the permanent refocusing of the projectile in the barrel.

The coaxiality of the projectile in the barrel is at first glance more problematic. Two scenarios must 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 faces and rear are significantly more resistant than the heart of the hoof. Thus, the phenomenon of recentering of 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 in relation to the barrel.

However, it is not always possible to ensure long guidance between the degradable shoe 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 in relation 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 assembly. projectile and degradable sabot around the center of the 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 “ahead” side and a lesser mass on the “lagging” side. The thrust pressure of the propulsion gases being relatively uniform, the acceleration on the “lagging” side will be greater than that on the “leading” side, which will have the effect of returning the projectile to a coaxial position with the gun.

It is at this point interesting to note that the appropriate shape for the base of the degradable sabot to fulfill this last condition of stability is quite close to a cone pointing towards the breech of the weapon. This shape makes it possible to satisfy the condition of coaxiality by short guidance when the master torque of the barrel is important (close to the breech) and to gradually move to long guidance as the diameter of the degradable shoe decreases by the taper of the barrel.

It will be noted that this shape can be complementary to a nozzle shape as described below. Two obvious advantages can be gained from this configuration.

The first advantage concerns the rigidity of the ammunition for guiding and chambering the ammunition in the barrel. Indeed, it is thus possible to reduce the transmission by the degradable sabot of 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. 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 of the nozzle of the case, the production of the degradable sabot is possible by injection of the material selected for the degradable sabot into an impression positioning the projectile and being closed by the 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, place of combustion of the propellant charge, and the projectile. This separation is achieved by means of a nozzle allowing gases to pass at supersonic speed inside the barrel.

To do this, several architectures are possible depending on the nature of the desired weapon and the accepted disadvantages:

If the weapon in question is a muzzle reloading weapon, the nozzle can be permanently fixed and formed directly by the barrel. In this case, the propellant charge can be placed through the muzzle of the gun if the propellant charge is in the form of a powder fine enough to enter 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 of the cannon. All types of conventional or under-calibrated projectiles are compatible with these 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 in the chamber and the projectile in 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 favored because of its practicality for loading operations, evacuation of shooting waste, unloading the weapon or cleaning the system.

Thus the nozzle can be formed inside a removable chamber relative to 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 or this nozzle can be formed inside a case forming an ammunition grouping the projectile and the propellant charge before firing. In addition, the projectile can be placed inside the ammunition case by complementarity between the shape of a base of the projectile or of one or more sabots and a portion of the nozzle as long as the ammunition is assembled.

Modeling the internal ballistics of firearms is well known and is based on a set of equations making it possible to determine the evolution of certain parameters in order to deduce the evolution of the speed and position of the projectile during firing. One of these equations represents the energy balance inside the gun and highlights the partial transfer of the energy released by the propulsive charge into kinetic energy of the projectile. The two phenomena limiting the transfer of energy are none other than the non-transformation of part of the thermal energy of the propulsion gases (which acts as a form of potential energy reserve allowing the continuation of propulsion of the projectile in the barrel, while the combustion of the propellant charge is completed), and the setting in motion of the propulsion gases (energy which is lost).

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

However, this would also forget that the quantity of energy available is concretely limited only to the quantity of propellant used (and therefore to the capacity of the chamber). Another more limiting factor for the performance of a gun – ammunition pair is none other than the maximum pressure the gun can bear. Thus a loss of efficiency in a phase of priming and start of propulsion of the projectile is not necessarily a handicap for the performance of the gun – ammunition pair if another phenomenon makes it possible to override the limitations of maximum pressure bearable by the gun .

In the barrel, the static pressure exerted on the internal walls of the barrel is linked to the static pressure at the breech as well as to the speed of the propulsion gases at the location of the barrel considered. The faster the propulsion gases, the more the static pressure exerted on the walls of the barrel decreases. In a traditional barrel, this results in a decrease in the maximum pressure reached as one moves towards the muzzle of the barrel. This is explained by the LAGRANGE hypothesis which indicates that the variation in gas speed is linear between the breech and the base of the projectile. This phenomenon is all the more marked as, 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 total available pressure (static pressure at the breech) is already exceeded while the projectile is still in the barrel.

For weapons adapted to rapid projectile firing, the barrel is made 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 bearable by the barrel 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 the breakage of the material used for the core of the barrel. In fact, the limit on 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 obstruction, a bursting barrel (which opens according to a crack without creating and dispersing fragments) is preferable to bursting behavior (brittle rupture with projection of shards).

Consequently, there is a major interest, for a weapon designer, in seeking to reduce the static pressure applying 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 the subject of studies.

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 reduce 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 greatest part of the cannon benefits from the advantages granted.

The device which allows the transition between a high pressure tank on the side of the breech (which we call chamber) and the barrel, where the pressure is lower and the speed of the propulsion gases is particularly high, is not nothing but a nozzle. This is characterized by a neck, the narrowest passage through which the propulsion gases pass, a convergent accelerating the propulsion gases to a sonic speed and a divergent bringing the propulsion gases to a supersonic speed.

In the initial state, the entire propellant charge is in the chamber which is closed by the neck of the nozzle 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. It is nevertheless necessary to take into account the pressure loss as the nozzle passes.

The end of the priming phase is characterized by a speed of passage of the propulsion 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 strong static pressure reigns 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 supersonic speed and lower static pressure.

These propulsion 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 exit of the nozzle and a dynamic component linked to the difference between the speed of ejection of the propulsion gases from the nozzle and the speed of the projectile in the barrel. Thus the pressure applying on 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 exit of the nozzle and a progressive recompression towards the pressure at the base of the projectile .

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

The construction and operating constraints of the barrel – ammunition pair mean that the thickness of the material of the barrel 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.

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

Of course other embodiments can be considered.

Claims (10)

Ammunition and weapon system, in which a projectile (7) is pushed by a propellant gas resulting 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 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 neck (3b) and a divergent (3c), one following the other towards the end open the barrel. System according to claim 1, 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 through the end rear and loading the projectile through the front end of the chamber. System according to claim 1, characterized in that the nozzle (3) is formed inside a case (13a) forming an ammunition (13) grouping the projectile and the propellant charge before firing. System according to claim 2 or 3, 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 shoes (8) and a portion of the nozzle (3). System according to any one of the preceding claims, characterized in that the propellant charge comprises an initiator composition (10c), a rapid combustion charge (10a) and a slow combustion charge (10b). System according to any one of the preceding claims, characterized in that at least one part (4a) of the barrel (4) has a conical section and in that the projectile (7) is associated with at least one sabot (8) degradable when moving it in this conical section part of the barrel. System according to claim 6, characterized in that the shoe (8) is made of a material depositing on the barrel (4) as it moves therein, to form a thermal protection layer (9 ) of it which is then evacuated. System according to claim 7, characterized in that the evacuation of the protective layer of the barrel (4) is obtained:

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

System according to any one of claims 6 to 8, 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, centralite, camphor, phthalate esther, nitroguanidine, nitroaminoguanidine, triaminoguanidine nitrate, N – butyl – N (2 nitroxyethyl) nitramine. System according to any one of claims 6 to 9, characterized in that the barrel (4) comprises a part of conical section (4a), followed by a part of rifled straight section (4b), the guiding of the projectile (7) being produced by the sabot (8) in the conical section of the barrel and by direct contact between the projectile and the barrel in the straight section thereof.