Since the conventional solid gun propellants have reached the saturation level in terms of energy output, a need exists for the development of high performance propellants for futuristic gun ammunition to propel hypervelocity projectiles. Hypervelocity guns are the guns having muzzle velocity in excess of 2000 m/s. Modern tank guns have muzzle velocity in the range of 1600 â€œ 2000 m/s. With continuous improvement in armour technology, improved weapons with high muzzle velocity are under development and are expected to be deployed in near future. In addition to armour defeating capability, high muzzle velocity endows the weapons with higher range, quicker response time and better accuracy. Also, hypervelocity projectiles are needed in modern aircraft guns to defeat fast moving aircraft and for simulation studies on nuclear weapons.
A considerable progress has been made on solid propellants, especially the propellants, containing cyclic nitramine, such as RDX. However, the higher percentage of RDX used in gun propellant formulation leads to problems associated with gun erosion. Hence, research and development activities were concentrated on the alternative concepts of the gun propulsion system, such as liquid gun propellant, rail gun, coil gun, electrothermal â€œ chemical gun, and electrothermal gun. Liquid gun propellants possess certain advantages over the solid gun propellants in respect of lower flame temperature, muzzle flash, continuous zoning capability, good storage stability, insensitivity, better logistics, and lower cost. However, encountered problems, such as gun design and ignition system along with combustion instability limit their application, and presently, no liquid gun propellant is in use. Electrically powered guns, though found to be attractive from the muzzle velocity point of view, storage of electrical energy is a major problem which has prevented its usage. It is, therefore, the solid gun propellants, based on the novel energetic ingredients, being considered as an ultimate choice for the futuristic hypervelocity projectiles. Solid gun propellants are preferred by the present ballisticians mainly due to the simple concept, lower cost, better thermal and chemical stability, and higher performance reliability. The present view gives a brief account of the gun propulsion systems, such as liquid gun propellant, rail gun, coil gun, electrothermal-chemical gun, and electrothermal gun. However, an emphasis has been made on the solid gun propellants based on the novel energetic ingredients as an ultimate choice for the futuristic gun ammunition.
But first of all let us see what a propellant is and where the real problem occurs for a conventional gun.
All guns and most rocket-powered weapons use solid propellants to provide their propulsion. The first solid propellant used by man was black powder in the thirteenth century. Black powder is no longer considered suitable for use as a propellant for several reasons: it burns incompletely, leaving large amounts of residue; it creates high temperatures resulting in rapid bore erosion; it creates great billows of black smoke; and it detonates rather than burns.
Gun powders or smokeless powders are the propellants in use today. This substance is produced by combining nitrocellulose (nitric acid and cotton) with ether and alcohol to produce a low explosive. Although called smokeless powders, they are neither smokeless nor in powder form, but in granule form. Smokeless powders may be considered to be classed as either single or multibase powders.
In single-base powders, nitrocellulose is the only explosive present. Other ingredients and additives are added to obtain suitable form, desired burning characteristics, and stability. The standard singlebase smokeless powder used by the Navy is a uniform colloid of ether-alcohol and purified nitrocellulose to which, for purposes of chemical stability, is added a small quantity of diphenylamine.
The multibase powders may be divided into double-base and triple-base powders, both of which contain nitroglycerin to facilitate the dissolving of the nitrocellulose and enhance its explosive qualities. The nitroglycerin also increases the sensitivity, the flame temperature, burning rate, and tendency to detonate. The higher flame temperature serves to decrease the smoke and residue, but increases flash and gun-tube erosion. Double-base propellants have limited use in artillery weapons in the United States due to excessive gun-tube erosion, but are the standard propellants in most other countries. Double-base propellants are used in the United States for mortar propellants, small rocket engines, shotgun shells, the 7.62-mm NATO rifle cartridge, recoilless rifles, and the Navy's 5"/54-caliber gun.
Triple-base propellants are double-base propellants with the addition of nitroguandine to lower the flame temperature, which produces less tube erosion and flash. The major drawback is the limited supply of the raw material nitroguandine. At present, triple-base propellants are used in tank rounds and are being tested for new long-range artillery rounds
Gun Propellant Configuration
Case guns are those that employ propellant encased in a metal shell, while bag guns are those that employ propellant charges packed in silk bags. The use of bags is confined to large guns where the total propellant powder required to attain the required initial projectiles velocity is too great in weight and volume to be placed in a single rigid container. By packing the powder grains in bags, it is possible to divide the total charge into units that can be handled expeditiously by one man
Now let us see some of the problems occurring in the guns by using the conventional propellants.
a) Erosion from Propellants
With the passing of corrosive primers, erosion from the propellant itself is undoubtedly your barrelâ„¢s greatest enemy. When the powder is ignited, it creates extremely hot gases under tremendous pressure. These two factors combine to create erosion, particularly in the throat area of the barrel.
Some older powders, such as DG Pyro or Hi-Vel#2, were very erosive due to their high nitroglycerine content and the resulting high flame temperature. When the 1903 Springfield was first introduced, the original loading of a 220 grain round-nose bullet at 2200 fps gave a useful barrel life of only 800 rounds. This was due to the high nitroglycerine content and resulting high flame temperatures of the powders then in use. As powder chemistry has improved, longer barrel life has been achieved. However, erosion from propellants will probably remain the No. 1 factor in barrel wear in the foreseeable future. This situation is unlikely to change until some radical improvements are made in the chemical makeup of the powder.
b) Improper Cleaning
It is a sad fact that with the great improvements in better barrel steels, non-corrosive primers, and less erosive propellants, probably as many of todayâ„¢s barrels are ruined by improper cleaning as by neglect. Careless use of a cleaning rod, failure to use bore or muzzle guides, improper use of harsh solvents, or the use of poor quality or badly maintained cleaning equipment all can do more harm to a firearm than no cleaning at all
c) Metal Fouling
Metal fouling may refer to either lead or copper buildup within the bore. This fouling is the result of the friction, pressure and high temperatures inherent in firing
d) Powder Fouling
Powder fouling is the result of the combustion of the powder that leaves an ash, or residue, in the barrel. In extreme cases, it may take the form of a carbon buildup. Powder fouling can generally be removed without too much difficulty by the milder solvents and a good scrubbing with a bronze brush.
So keeping in mind the defects with the conventional propellants and propulsion system we can now move across to some of the non conventional propulsion systems its advantages and its disadvantages.
1) LIQUID GUN PROPELLANTS
Interest in liquid propellants for guns has been generated after their use in rockets. Research has been carried out in the USA for their developments. Liquid propellants have been classified as mono propellants [Iso propyl nitrate(IPN),hydroxyl ammonium nitrate(HAN),Me nitrate] and bio propellants [red fuming nitric acid(RFNA)+Mono methyl hydrazine(MMHN),(liquid N2+liquid O2)].Similarly, bio propellants have been classified as hyper golic[RFN + unsymmetrical di methyl hydrazine(UDMH)] and non hyper golic[(liquid O2+liquid H2)(H2O2 + NH3)].Considering the nature of gun systems, the use of cryogenic liquid propellants is out of question. Similarly, material constraints and stability have resulted in the rejection of potential candidates like RFNA and H2O2.Main requirements placed on a potential candidate are high density, mall variation of density with temperature, high specific heat and thermal conductivity and boiling point, less viscosity, thermal stability, etc.Ultimately, HAN, Triethanol ammonium nitrate (TEAN) and water mixture has been selected as potential candidate for liquid gun propellant
Several designs for the combustion chamber of the gun systems have been prepared. Bulk loading gun systems were the first to appear. However, increasing incidents of combustion instability and erratic behavior led to the regenerative loading gun systems. Traveling charge gun system is the latest in the chamber design. It is as shown in the figure below. Inspite of the potential advantages of the liquid gun propellant, the concept has not been fully emerged. This is mainly due to lack of suitable gun barrel for the liquid propellant evaluation, investigation of the suitable ignition systems, and means to resolve the combustion instability.
2 ) RAIL GUN
A railgun, also known as a Gauss gun, is a form of gun that converts electrical energy into projectile kinetic energy, rather than the more conventional chemical energy from an explosive propellant.
They use the force produced by a magnetic field to propel a projectile that is initially part of the current path. The current flowing through the rails sets up a magnetic field. The current flows through the projectile perpendicularly to the current in the rail. Conveniently, this allows the resultant force to direct the projectile along (parallel to) the rails.
Theory and construction
The theory and construction of a railgun are quite simple at first sight, but very complex beneath.
An electrical current, when in a magnetic field, experiences a force perpendicular to the direction of the current and the direction of the magnetic field. This is the principle behind the operation of an electric motor, where fixed magnets create a magnetic field, and a coil of wire is carried upon a shaft that is free to rotate. When electricity is applied to the coil of wire a current flows, causing it to experience a force due to the magnetic field; the wires of the coil are arranged such that all the forces on the wires act to make the shaft rotate, and so the motor runs.
A railgun is even simpler than a motor. It consists of two parallel metal rails (hence the name) which are slotted on the inside so that a metal projectile can slide between the rails. At one end, the rails are connected to an electrical power supply. When the projectile is inserted between the rails (from the end connected to the power supply), it completes the circuit. Electrical current runs from the positive terminal of the power supply up the positive rail, across the projectile, and down the negative rail back to the power supply again.
This flow of current makes the railgun act like an electromagnet, creating a powerful magnetic field in the region of the rails up to the position of the projectile. But since the rails and projectile are carrying an electrical current through this magnetic field, they experience a force; and it so happens that when you run through the maths, the force is trying to push the rails and projectile outwards. Since the rails are firmly mounted they cannot be pushed apart, but the projectile is able to slide up the rails away from the end with the power supply.
If you happen to do this with a very large power supply, providing a million amperes or so of current, then the force on the projectile will be tremendous, and by the time it leaves the ends of the rails it can be travelling at many kilometres per second.
The complexity in railgun design comes from:
1. The need for strong conductive materials to build the rails and projectiles from; the rails need to survive the violence of an accelerating projectile, and heating due to the large currents involved and friction. The force exerted on the rails consists of a recoil force - equal and opposite to the force propelling the projectile, but along the length of the rails (which is their strongest axis) - and a sideways force caused by the rails being pushed by the magnetic field, just as the projectile is. The rails need to survive this without bending, and be very securely mounted.
2. Power supply design. The power supply must be able to deliver a large current for a tiny amount of time, so capacitors and compulsators are both being pursued; most other power supplies are designed to provide constant power levels for long periods, which is a very different design requirement.
3. Electromechanical design. What is the optimum distance between the rails, the optimum size of the rails, and the optimum shape for the projectile The shape of the conductors influences the shape of the magnetic field. Ideally, the magnetic field should be as strong as possible in the region of the projectile in order to get the most acceleration. But anything that makes the conductive path longer increases its resistance, and so less current flows. Computer simulation and physical experimentation are being used to try to find optima.
Railguns as weapons
Railguns only fire bullets, not shellss. Shells depend on their arrival at the target being more violent than their launching, so they can be detonated by impact without detonating in the barrel of the gun. However, being fired from an anti-tank railgun can be more violent than hitting a tank (the projectile accelerates to maximum velocity in the space of a metre or two, but when it hits the tank it punches straight through and decelerates for several metres), so the detonating mechanism for a shell would have to be fairly complex (and thus expensive, and prone to failure in dangerous ways). The railgun is still an effective weapon as the raw kinetic energy of a railgun projectile will not only punch through armour plating with impunity, it will spray vaporised metal carried on a sizeable shock wave which incinerates the interior of the target (and any occupants) .One could construct a low-velocity railgun that fired shells, but there seems to be little interest in doing so to date; existing chemical propellant systems have that niche quite securely filled, although it is perhaps likely that future railgun artillery would also have a low-velocity shell firing mode for indirect fire and delivering chemical or biological payloads.
The United States military is funding railgun experiments. At the University of Texas' Centre for Electromechanics, military railguns capable of delivering tungsten armour piercing bullets with kinetic energies of nine million joules have been developed.  Nine million joules is enough energy to deliver a kilogram of projectile at three kilometres per second - which will tear a tank to pieces in a single shot. Naval forces are interested in railgun research, too. Current ship guns sit on top of a large room called a magazine, which is full of shells for the gun to fire. If a shell from a hostile ship should happen to penetrate into the armoury and explode, it is quite likely to cause all of the shells in the magazine to detonate, usually destroying the ship. However if the ship is instead equipped with railguns, all it needs to store to feed the gun are the tungsten bullets, which are much more compact than shells - and the electricity can be supplied from the ship's engines, perhaps buffered in capacitors. These things will explode much less violently than a room full of shells if hit.
Now some of the different classification of the rail guns
The Segmented Rail gun
The length limitation imposed by rail resistance and rail inductance can be circumvented by simply subdividing a long rail gun into short segments, each fed by an independent local energy source. This will of course involve certain commutation problems as the projectile transitions between segments, but will permit using part of the energy stored in each segment to energize the subsequent segment. The segmented rail gun seems promising for launching large masses such as aircraft at low acceleration. In very long launchers, the use of multiple independent energy supplies will have other advantages as well.
The Helical Rail gun
The rail gun is in essence a single-turn motor. A multi-turn rail gun would reduce the rail current and the brush current by a factor equal to the number of turns. It therefore seems worth-while to study a "helical rail gun". In this hybrid device, the two rails are surrounded by a simple helical barrel, and the projectile or re-useable carrier is also helical. The projectile is energized continuously by two brushes sliding along the rails, and two or more additional brushes on the projectile serve to energize and commute several windings of the helical barrel direction in front of and/or behind the projectile. The helical rail gun is in fact a cross between the rail gun and the mass driver.
Peaceful uses of railguns
There is interest in using railguns as mass drivers for space exploration and mining. They would be useful for launching bulk ores into space, particularly from low-gravity bodies such as moons and asteroids; electrically powered from solar panels, they would not require any consumables such as rocket fuels.
Rail guns have been proposed for use in delivering projectiles to space, especially from bodies without atmospheres (such as the Moon). Its main competitors are coil guns and ram accelerators.
Also, railguns may be used to initiate fusion reactions, by firing pellets of fusible material at each other. The impact would create immense temperatures and pressures, allowing nuclear fusion to occur. However current railguns are not yet sufficient to achieve the energies required.
3) COIL GUN
The oldest form of electromagnetic guns built was the coil gun. The development of coil gun is reported to have started in 1845.The credit for the first patent on coil gun went to Prof Kristian Birkland of the University of Oslo. He accelerated 500 gm projectile to a velocity of 50 m/s.German scientist Dr.Jorachim Hansler continued the same work in 1944.A velocity of 4.9 km/s for projectile of mass 1.3 gm was achieved by soviet scientists. The coil gun is as shown in figure. The gun consists of fixed accelerated coils. When these spools are electrified sequentially, a traveling magnetic field arises that induces a current in the projectile coil. As a consequence, the traveling magnetic field exerts the Lorenz force on the projectile coil current, thus accelerating the projectile.
The basic operating principle of the coil gun is as follows. A coil gun consists of two interacting parts, the coil and the projectile. Suppose we take something like a short rod of iron or steel and place it next to the coil, what happens The rod is attracted into the coil. This attraction occurs because the coil magnetizes the rod, effectively creating two separate magnets. The rod is magnetized in the same sense as the coil so the end of the rod which faces the coil 'sees' an opposing pole. Regardless of which end of the coil the rod is placed, it will experience an attraction since the coil will always magnetize the rod in the same sense as its own magnetic field. It would be a different story if the rod was an independent magnet. If this were the case the direction of the current and the orientation of the rod could result in either an attraction or repulsion. We can look at this in a little more detail by considering the interaction of the flux from the rod and the current in the coil. The diagram below shows a coil and rod in close proximity. The rod is magnetized such that it 'sees' the opposite pole when it faces the coil.
It's almost impossible to calculate a value for the attractive force by applying the force equation, the complexities involved would likely result in 'ball park values' at best. There would be far too many simplifications required to get an accurate value. What you would need to do is integrate the force value obtained from each elemental part of the coil. This would require some estimation of the flux distribution which isn't possible using analytical maths. This is where we need to turn to numerical field solution programs such as Quick field or FEMM. These allow us to accurately determine the flux distribution and forces in a static magnetic system.
Unfortunately things aren't quite that simple. Solving for a static situation ignores a very important mechanism of electromagnetics, namely induced voltage and current. As the projectile accelerates into the coil, the flux linkage increases generating an induced voltage in the coil which opposes the supply voltage. This tries to reduce the coil current and the magnetic field which, in turn, induces a voltage that tries to maintain the coil current. As you can see, things get a bit complicated. In many instances, the magnetostatic solution may not be a good indicator of the dynamic performance. An exception to this is the situation in which the induced voltage is small compared to the supply voltage, such as a slowly moving projectile. In this instance the current will only be affected slightly. This means that a series of magnetostatic simulations could be used to produce a rough estimation of the muzzle velocity. An example of this comparison can be found in the results section.
The main difference between the rail gun and the coil gun lies in the production of the current loops. In the coil gun, there are a number of loops that supply the same magnetic force to the projectile, whereas in the rail gun only a continuously changing current is produced. This makes the coil gun more efficient than the rail gun, but is also more complex. Moreover, the coil gun presents problems in high current switching. Therefore todayâ„¢s research is focused on rail gun.
This is a latest prototype of a coil gun.
4) ELECTROTHERMAL GUN
The third basic type of electrically powered gun is the electrothermal gun. The concept of an electrothermal gun using plasma rather than explosively released chemical energy from a combusting solid propellant charge was first considered in Germany in 1945.However, yolter (General Electric Co) claimed the first patent in 1956. Bioxsom achieved a velocity of 2990 m/s for nylon spheres 13 mm diameter .The electrothermal gun exists in several versions. In the simplest version, the gun consists of a conventional barrel with electrodes, leading to a plasma burner mounted on the breech end of the weapon. A voltage across the plasma burner electrodes creates an arc that vaporizes material ploy-ethylene, place between electrodes .The vaporized material is superheated until it becomes a high pressure plasma which accelerates the projectile. The electrothermal gun is shown in figure.
The electrothermal gun is expected to yield higher projectile velocity than the conventional guns. However, the hot plasma may also increase erosion and shortens the gun barrel life. The other problem associated with the present electrothermal gun is the enormous weight and size of the electrical power supply.
Electric propulsion (EP) provides much lower thrust levels than conventional chemical propulsion (CP) does, but much higher specific impulse. This means that an EP device must thrust for a longer period to produce a desired change in trajectory or velocity; however, the higher specific impulse enables a spacecraft using EP to carry out a mission with relatively little propellant and, in the case of a deep-space probe, to build up a high final velocity
5) ELECTROTHERMAL CHEMICAL GUN
Improve the lethality of direct-fire ground systems by providing the technology to significantly increase available muzzle energy. A well-established technique to improve penetration is to increase energy delivered to the target. One option is to provide larger-caliber cannon. However, this approach is not supported by the user as the increased-caliber weapon requires significant vehicle modifications. Electrothermal-chemical (ETC) propulsion offers the possibility of providing increased lethality without increasing gun size. As such, the battlefield advantage of direct fire would be maintained without major changes in the cannon or ammunition envelope.
ETC will enhance the lethality of direct-fire cannons by providing a significant increase in muzzle energy within the existing weapon envelope. The ETC cartridge is essentially identical in mass and geometry to current ammunition; thus, no changes to ammunition storage or handling are required
The electrothermal chemical gun is an innovative hypervelocity propulsive system whose energy comes from an external energy source (i.e., electrical energy input) as well as an internal energy source (i.e., chemical energy).The electrical energy is discharged to the electrothermal chemical gun by a separate device called pulse forming network (PFN).The chemical energy, on the other hand, is released through combustion of the working fluid (ie, liquid propellant) in the gun chamber. The electrothermal chemical gun provides several advantages over the conventional solid propellant and the liquid propellant guns. For example, the electrothermal gun system can produce a higher muzzle velocity because the propulsive energy is not limited by the size of the combustion chamber and the amount of liquid propellant (i.e., the ratio of the projectile mass and the propellant charge) .As such, the muzzle velocity of an electrothermal chemical gun could exceed 2000 m/s. The electrothermal chemical gun also provides a better controllable operation, since the combustion rate of the liquid propellant can be regulated by the electrical energy input, thus preventing runaway combustion and abnormal pressurization. A typical electrothermal chemical gun is as shown below
A typical electrothermal chemical gun consists of four major parts. These include the PFN, the plasma generating cartridge, the gun barrel and projectile, and the working fluid (liquid propellant).The primary function of the PFN is to store and discharge the electrical energy in to the plasma generating cartridge. The electrical energy is used to convert the wall material in the plasma generating cartridge to high temperature plasma in the discharge process. The plasma fed into the gun chamber decomposes the working fluid, resulting in the pressure rise, and thus, the subsequent acceleration of the projectile takes place under the influence of the generated propulsive energy .Conceivably, by tailoring the PFN discharge process and selecting a suitable working fluid, it is possible to achieve a high muzzle velocity while maintaining a low breech pressure in the electrothermal chemical gun.
The electrothermal chemical gun was developed and subsequently improved by designers at the FMC and GT-Devices in the early 1980â„¢s.A muzzle velocity of 2750 m/s for a 30 mm gun was reported by researchers, where as a muzzle velocity of 2800 m/s for a projectile of 25 gms was reported at GT-Devices. Several studies have been conducted on the fundamental features of the electrothermal chemical gun, including the thermochemical properties of various working fluids, the PFN circuits and batteries, and plasma/ working fluid interaction in the electrothermal chemical gun chamber.Theoritical models have also been developed.
Technical barriers for ETC include insensitive high-energy, high-density propellant formulations and geometries; design of plasma generators for effective coupling of electrical energy into propellants; and control of propellant temperature performance effects
So having gone through the unconventional gun systems and liquid gun propellants, their advantages and their disadvantages we shall move to some of the conventional propellants and their improvements.
SOLID PROPELLANTS BASED ON NOVEL ENERGETIC INGREDIANTS
In view of many problems associated with the advanced propulsion systems, i.e., liquid gun propellants and electrically powered guns, the gun systems have not emerged fully on the scene in spite of their high energetic potential on the terms of their high energetic potential in terms of muzzle velocity. Hence, the attention of the ballisticians has currently been refocused on the solid gun propellants containing novel energetic ingredients, and active research is being carried out all over the globe.
Here are some of the energetic ingredients that can be added to the propellants to improve their muzzle velocity.
The nitramine HMX is a well-known energetic material used as a high explosive. Together with the German Fraunhofer Institute of Chemical Technology (ICT), TNO-PML developed crystallization processes with which high quality crystals can be produced. BICT water gap tests, both performed at ICT and TNO-PML, have shown that these materials are much less sensitive towards shock initiation. A direct relation has been found between the (mean) density of the crystals and the sensitivity of an explosive item in which these crystals are incorporated. More recently, flyer impact initiation tests were carried out at TNO-PML.).
HNF is used as a high performance oxidizer in composite solid propellants. HNF is produced on pilot scale by Aerospace Propulsion Products by (APP) in The Netherlands. In cooperation with this company, the crystallization of HNF was investigated in order to improve its shape from a needle to a more compact, isomorphic shape and to control the mean size of the crystals. Hereto different crystallization techniques like cooling, evaporative and drowning-out crystallization were applied using a range of different solvents or solvent/non-solvent combinations.
HNF can be applied as a high performance oxidizer in both composite solid propellants and monopropellants (liquids). Due to the fact that it does not contain any chlorine, it produces clean exhaust gases during combustion. Its performance is superior compared to conventional (e.g. AP/HTPB based) or ADN based propellants.
Figure 8, HNF Crystals
HNS is an energetic material which can be used at fairly high temperatures. Different grades exist (I, II, III and IV) which all exhibit different, characteristic properties. For instance, HNS IV consists of very small particles with a high specific surface area in the range of 5 25 m2/g. At TNO Prins Maurits Laboratory a special crystallization process was developed with which HNS IV can be produced (see the scanning electron micrograph below). From this material pressed pellets can be made for application in slapper detonators. In cooperation with the research group 'Properties of Energetic Materials' the detonation characteristics are being assessed.
Figure 9, HNS Crystals
CL-20 is a relatively new high explosive in the nitramine class. CL-20 may crystallise, depending on the conditions, in five different crystal structures or polymorphs of which the -phase is stable at room temperature (up to 60 C) and has the highest density (~2.0 g/cm3). Its detonation properties are superior to those of HMX and RDX.
It appears that the proper crystallisation of CL-20 is not very easy. Commercially available grades consist of agglomerates rather than individual particles. At TNO Prins Maurits Laboratory we were able to produce nicely shaped CL-20 crystals.
Figure 10, CL-20Crystals
Figure 11, CL-20 Crystals
Ultra High Energy Gun Propellants
A series of ultra high energy azide containing gun propellants have been formulated in the USA, wherein it is shown that propellants, having a force constant more than 1451 j/g at flame temperature less than 4000 k, is possible. The propellant comprises 25-35 percent NC (Nitrocellulose) based binder and a combination of azide compounds.
High Energy Propellants Based On Metallic Powder
Incorporation of aluminium powder into the conventional gun propellants was suggested to improve the ballistic properties of single- base and double- base propellants. The experimental investigations reveal that addition of aluminium in the conventional propellants increase the force constant, and consequently, the muzzle velocity of a projectile. It decreases the molecular weight of the combustion gases and keeps the temperature within the safety limits of the gun. The optimum content of the aluminium was found to be not more than 5-8 percent. With such a percentage of aluminium, it is expected that the flame temperature will increase up to 3100-3300 k, the force constant will increase 15-20 percent and muzzle velocity by 4-8 percent. This method of incorporating aluminium leads to reduction in the molecular weight of the combustion gases due to deoxidation of CO2 to CO.
Even though the modern concepts of the gun propulsion system, such as liquid gun propellant and electrically operated guns are highly promising for propelling the futuristic hypervelocity projectiles, the same have not emerged on the global scene due to acute problems associated with these. In view of this, the solid gun propellants based on the novel energetic ingredients like CL-20, HMX, HNS, HNF etc. have been recommended to meet the objectives of the futuristic gun ammunition. Even though these novel energetic ingredients are currently being used in the experimental formulations, it is expected that these will form the basis for the futuristic high energy propellants. Future research in advanced solid gun propellants will also take place using propellant formulations containing compounds like azide, nitramine, triaminoguanidine, and hydrazine, which will produce low molecular weight combustion gases. Such fundamental research is essential for the development of futuristic hypervelocity guns. Hence, muzzle velocity in the range 2000-2500 m/s is expected to be achieved using solid gun propellants without restoring to rather unconventional methods of the propulsion like liquid gun propellant and electrically operated guns.
1) R.S.Damse and Amarjit Singh, Advanced concepts of the propulsion system for the futuristic gun ammunition, Defense Science Journal, Vol .53, No.4, pp.341-350, October 2003