in order that this invention may be more readily understood and put into practical effect , reference will now be made to the accompanying drawings which illustrate typical embodiments of the invention , wherein : fig1 to 4 diagrammatically illustrate typical barrel assemblies according to this invention ; fig5 illustrates a pod of grenade firing barrel assemblies ; fig6 is a diagrammatic cutaway end view of a cluster of barrels ; fig7 illustrates a typical application of the present invention ; fig8 illustrates a further application of the invention utilising an unmanned aerial vehicle ; fig9 is an underside view of one of the pod carriers of the aerial vehicle of fig8 ; fig1 is a diagrammatic cross - sectional view of a pod of splayable barrel assemblies , and fig1 illustrates a typical application of one aspect of this invention . the barrel assembly 10 illustrated in fig1 has multiple grenade carrying projectiles 11 of substantially known form loaded in a rifled barrel 12 to impart spin upon firing for activating the arming device . however the rupturable propellant cup or high pressure chamber 13 is fixed to the projectile 11 for dispensing from the barrel with the projectile to clear the barrel for the following firing . this chamber exhausts through exhausts 14 into the barrel space between the stacked projectiles 11 which forms the low pressure chamber 15 . each projectile 11 includes a projectile body 17 , which in this embodiment is a grenade housing 18 housing a grenade 22 , and a trailing sleeve 19 which is retained thereon for limited relative axial movement . the sleeve 19 has a head part 20 which tapers inwardly to an internal collar 21 which extends into a complementary shaped external recess 23 formed in the grenade housing 18 . the sleeve 19 tapers outwardly at its rear end 24 to engage over a corresponding tapered leading face 25 of the projectile 11 stacked therebehind . in use , as disclosed in our earlier inventions , loading of the projectiles 11 into the barrel 12 forms a wedge type seal 26 between the leading end of the sleeve 19 and the trailing tapered face 27 of the head part 20 which prevents the ignition of the leading propellant spreading about the grenade housing to the propellant in the following round . loading also effects a further wedge type seal 28 between the rear end 24 and the leading face 25 and expands the rear end 24 into operative sealing engagement with the barrel 12 . thus the sleeve forms a barrier to spreading of ignition thereabout to propellant charge in the trailing round . firing of the leading projectile 11 releases the leading seal while maintaining the sleeve 19 captive with the grenade housing 18 but maintains an operative seal at the rear end of the sleeve with the barrel 12 . as the pressure propelling the projectile is relative low , in the order of 3000 psi , only minimal sealing is required . the barrel assembly 30 illustrated in fig2 is similar in configuration to that illustrated in fig1 , the main difference being the manner in which the sleeve 31 is retained on the grenade housing 32 and the configuration in which the sleeve 31 confines a smaller low pressure chamber 33 between adjacent projectiles 35 into which the high pressure chamber 36 exhausts through ports 38 . the sleeve 31 also has a shallow wedge 34 at its leading end which may be expanded into sealing engagement with the barrel during loading but which is released upon firing during the initial forward movement of the housing 32 and upon subsequent impact with the back face of the return 27 . the barrel assembly 40 illustrated in fig3 is also similar in configuration to that illustrated in fig1 , the main difference being the wedge sealing angles α and β between the trailing sleeve 31 ′ and the grenade housing 42 . in this embodiment which is more suited to low pressure low muzzle velocity applications , the opposed ends of the trailing sleeve 31 ′ formed by the sealing angles α and β of between 30 ° and 55 ° are sufficiently blunt as to resist outward splaying into sealing engagement with the barrel under the influence of propellant pressures . typically these would be in the order of 3000 psi to 5 , 000 psi with muzzle velocities of about 70 m / sec and 250 m / sec respectively . it will be seen that the bulbous nose part 43 of the projectile body 42 is hollow for carrying explosives , or fuel as referred to in relation to fig1 . as in the embodiments illustrated in fig1 and 2 the propellant 37 in the high pressure chamber 46 is selectively ignited to expel high pressure gases through the trailing ports 39 into the low pressure chamber 33 ′ by a detonator 16 triggered through an electrical circuit which uses the projectile column as one part of the circuit , the barrel 41 being made of insulating material or so lined and with the circuit completed by an imbeded insulated wire 29 leading from the primer 16 to a contact 29 ′ on the projectile surface which is aligned when loaded , with a complementary contact 44 supported in the barrel 41 . alignment of the contacts can be achieved in a barrel and projectile located by rifling grooves during the loading process . in a non rifled design , the use of a annular contact in the barrel wall can achieve a similar result . the barrel assembly 45 illustrated in fig4 substantially corresponds in mechanical configuration to the fig3 embodiment . however the high pressure chamber 46 is disposed externally of the barrel and communicates with the low pressure chamber 47 through aligned ports 48 and 49 in the wall of the barrel 50 and trailing sleeve 51 respectively . as shown cutaway in fig6 the high pressure chamber 46 is of such configuration that it will fit snugly into the space bounded by the adjacent side walls 52 and 53 of further barrels of a cluster of barrels 45 . further in each of the above embodiments the sleeve provided a relatively broad cylindrical surface which engages closely with the bore of the barrel so as to assist in preventing passage of ignited gases between the sleeve and the barrel . further in the embodiments illustrated in fig2 and 4 the inward projections on the sleeve engage within complementary recesses formed in the housing and provide a labyrinth type seal across the inner face of the sleeve . in all the above embodiments the propellant in the high pressure chamber is adapted to be ignited by electronically controlled ignition means as known from our earlier international patent applications . as illustrated in fig5 , a typical weapon according to this invention includes a cluster of barrel assemblies 55 adapted to fire grenades 56 and contained in a pod 57 such that a selected number of near simultaneously exploding grenades may be fired at a time . the grenades 56 are fired selectively from the pod 57 by computer control . the weapon in the illustrated embodiment contains ninety - eight barrel assemblies each containing stacked grenades 56 and having selectively ignitable internal or external propellant charges . in this embodiment the pod 57 is carried on a turret mounting 58 whereby the barrels may be swivelled about vertical and horizontal axes for aiming purposes . suitably 40 mm grenades 56 are used as the projectiles because of their ready availability . the grenades 56 are fired selectively by computer control from the pod 57 which is envisaged will contain ninety - eight barrel assemblies each containing stacked grenades 56 and having selectively ignitable internal or external propellant charges . the grenades 56 may be selectively fired to form a controlled impact array of exploding grenades on the zone to be investigated . by way of example , using such a barrel assembly in a pod of ninety - eight 40 mm barrels that would measure approximately 350 mm × 700 mm in cross section , with each barrel loaded with six projectiles , and with each projectile similar in size to a conventional 40 mm military grenade , a barrel length of 900 mm would be required and the assembly would provide a projectile capacity of five hundred and eighty - eight projectiles . this configuration would be suitable for seismic applications requiring a short range such as for delivering projectiles from downwardly facing barrels . for longer range delivery fewer projectiles would be accommodated in each of such barrels or longer barrels would be used and more propellant would be utilised to achieve higher muzzle exit velocities . the maximum rate of fire per barrel is expected to be as high as 20 , 000 projectiles per minute and the maximum rate for the combined ninety - eight barrels would be 1 , 960 , 000 projectiles per minute , assuming that all barrels are fired simultaneously at the maximum rate . for a ninety - eight shot burst firing the leading round from each of the ninety - eight barrels , the rate is infinitely variable and which may be a ninety - eight shot burst fired at a rapid frequency . the above ninety - eight barrel pod is one example of a range of performance specifications that could be available . different performance specifications can be generated by altering the component parts of the pod . for example , a pod may be preloaded such that the nature and weight of the explosive and / or projectile may vary between individual barrels in the pod or within a barrel . a plurality of such pods 57 may be carried on a vehicle and arranged whereby each pod 57 may be selectively directed toward a desired target and fired at a selected rate . alternatively the pods 57 may be fired collectively at a single target . in the embodiment illustrated in fig7 , the grenades 56 are fired downwardly from a pair of such pods 57 , only one of which is shown , carried by a helicopter 58 to provide bombing coverage of a tract of land . the density of such bombing and the area of land covered by the bombing can be controlled by controlling the variables such as rate of fire , elevation and speed of the aircraft . the unmanned combat aerial vehicle 60 illustrated in fig8 and 9 carries six such pods 57 in cases 61 under the wings 62 at each side of the fuselage 63 . it is envisaged that each pod could contain six 40 mm grenade pods with one hundred barrel assemblies per pod and with six grenades in each barrel . this would provide a loaded capacity of 7 , 200 grenades representing a payload of about 3 , 600 lb . in this embodiment aiming of the barrels containing the grenades 56 would be achieved by remote control of the aircraft which may carry a video camera or the like for assisting its control remote from an operator . the projectile firing pod 70 is illustrated diagrammatically in fig1 and cutaway to illustrate only two barrel assemblies 71 of the type described which would be contained within a rectangular pod housing 72 in spaced apart relationship suspended from an upper wall 73 from respective ball type mountings 74 . each barrel assembly 71 extends downwardly through the fixed ball - like mountings 74 to direction control means 75 which in this embodiment is able to individually or collectively control the barrel assemblies 71 for movement to an inclined attitude at one side or the other of their normal vertical position illustrated or to the front or back of that normal vertical position or to a combination of those attitudes as required . for this purpose , each barrel assembly is provided with a cylindrical positioning block 78 supported rotatably about its lower end for eccentric motion about the axis of each barrel assembly . an intermediate wall 80 is apertured to closely receive each cylindrical positioning block 78 . the vertical position of the intermediate wall 80 is controlled by a hydraulic ram 81 supported on the base wall 82 of the pod housing 72 . extension and / or retraction of the ram 81 will move the intermediate wall 80 in a vertical direction restraining the respective apertures for movement along respective fixed axes so that , in the illustrated barrel assemblies , as the intermediate wall 80 moves downwardly , the lower ends of the barrel assemblies 71 will be moved inwards towards one another - causing the barrel assemblies to splay outwardly relative to one another due to the fixed spacing of their upper ball mountings 74 . accordingly , it will be seen that by controlling the position of the hydraulic ram 81 the barrel assemblies can positioned with their axes vertical and parallel , inclined to the vertical and parallel , or with their axes in a splayed attitude . each positioning block may be selectively rotated about the lower end of the barrel assembly on which it is mounted by extension or retraction of a further hydraulic ram 84 supported on the intermediate wall 80 and extending to a track 83 in the outer side wall of the respective positioning block 78 . the configuration of the track could be such that normal vertical movement of the intermediate wall 80 will not cause rotation of the blocks 78 in the direction of the arrow 85 unless the ram 84 is extended or retracted . it will be seen that the vertical ram 81 connected to the intermediate wall 80 acts collectively on all barrel assemblies so as to move them in unison while individual horizontal rams 84 are provided for each barrel assembly 71 . these rams 84 may be individually controlled independent of the ram 81 . thus , for example , whereas the positioning blocks 78 are illustrated in the drawings arranged at opposing offsets with respect to the illustrated barrel assemblies 71 , one of the positioning blocks could be rotated through 780 ° by its ram 84 so as to arrange both cylindrical positioning blocks 78 with their axes parallel to one another and at an identical offset to the axes of the associated barrel assemblies 71 . in this configuration , operation of the vertical ram 81 would pivot both barrel assemblies identically to one side or the other from the vertical , while at intermediate positions of one positioning block 78 relative to the other , splaying of the barrel assemblies could be achieved . of course , both sets of rams 84 and 81 could be actuated simultaneously and be controlled by a suitable controller 86 to achieve a significant variation in target direction and spread of the fall of projectiles fired therefrom . in addition , the configuration of the impact pattern may be varied within a set zone . the barrel assemblies may also be controlled to provide a limited amount of turreting to achieve long range tight grouping of projectiles . it will be seen that a projectile firing pod which may have an in - built remote controller 86 , which may receiving information from orientation sensors mounted on or associated with the barrel assemblies or from the ram positions , may be readily delivered and deployed very quickly to a site even though that site may be off - level and thereafter remotely controlled to fire projectiles at a common or at varying inclinations to the vertical to achieve the desired fall of projectiles at the impact zone . also , the proportions of the impact pattern may be varied or maintained constant with varying target spread areas . the drives for rotating the blocks 78 could be independent of the intermediate wall 80 , such as rotary drives with flexible or splined drives to the base of the barrel assemblies . further the base 82 could be inclined to the side walls or be jackable to an inclined position to provide a coarse inclination toward the target zone with final aiming control achieved remotely by the direction control means 75 . a typical application of pods described above , as illustrated in fig1 could be to fire a selected array of projectiles containing fuel to be dispersal therefrom in a controlled manner and pattern to form a defined fuel / air cloud to be detonated by further projectiles fired from the same pod or pods . for example the fuel containing projectiles could form a fuel / air cloud 90 in a substantially conical shape and detonation could be effected simultaneously from a plurality of locations 91 about the upper portion of the cone to form a focused explosion directed to the desired target 92 . the size and height of the cloud could 90 be selected to deliver high pressure shock waves to a localised area . this could be utilised to explode a land mine field , as a lethal anti - personnel attack or , by further elevating the cloud 90 to provide a concussive non - lethal attack against ground troops . it will of course be realised that the above has been given only by way of illustrative examples of the invention and that all such modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of the invention as is defined by the appended claims .