Abstract:
A modified 40 mm grenade round designed to breach doors without throwing a substantial amount of shrapnel into a building&#39;s interior. The modified round includes a standoff device located on its forward end. The standoff device detonates the explosive charge within the projectile before the nose of the projectile actually strikes the target. This early detonation throws a pressure wave again the door&#39;s exterior, forcing the door inward. Shrapnel produced by the detonation remains primarily outside the door. Thus, the modified projectile is able to blow open a door without throwing a significant amount of shrapnel into a building&#39;s interior.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the field of projectile delivery systems. More specifically, the invention comprises a standoff device configured to detonate the explosives in a projectile before the nose of the projectile strikes a target. 
     2. Description of the Related Art 
     Although the present invention can be applied to many different types of projectiles, it was primarily developed as a component of existing 40 mm grenade weapons (such as the U.S. Army&#39;s M-433).  FIG. 1  depicts prior art 40 mm grenade round  10 . Its two main components are case  12  (which houses the propulsion system) and projectile  14 . The grenade round is designed to be fired from a variety of weapons. One example is the U.S. Army&#39;s M-203 grenade launcher which is typically slung beneath the barrel of a rifle such as the M-16A2. 
     The launching of a 40 mm grenade involves the same principles as a conventional rifle cartridge. The main difference, however, is the size and mass of the projectile. A typical shoulder-fired military weapon launches a projectile weighing less than 30 grams at a relatively high velocity (700-1,000 meters per second). In contrast, a 40 mm grenade weapon launches a projectile weighing over 200 grams at a relatively low velocity (70-80 meters per second). Thus, while the operating principles between the two types of weapons are the same, they can be said to operate in different regimes. 
     The unified 40 mm grenade round  10  is placed in the launching weapon and then fired. Case  12  remains within the weapon. Projectile  14  is propelled down the weapon&#39;s bore. Rifling ring  26  engages internal rifling on the firing weapon&#39;s bore and spins the projectile in order to stabilize it in flight. 
     The leading end of the projectile assumes the form of ogive  28 . Those skilled in the art will know that the term “ogive” sometime refers to a specific pointed shape used for missile nose cones. However, the term is also more broadly used to mean the nose portion of any flying projectile. In this disclosure, “ogive” is given the latter meaning. The ogive generally contains the arming and detonating mechanisms. The volume between the ogive and the rifling ring typically contains the explosive. 
       FIG. 2  shows the same 40 mm grenade round of  FIG. 1  cut in half to reveal its internal details. Projectile  14  includes a hollow volume defined by the combination of ogive  28 , casing  36 , and aft closure  38 . These three components are joined together by suitable means, such as threaded engagements. 
     Explosive  34  is contained within casing  36 . Fuse assembly  30  is contained within ogive. It activates spitback detonator  32 , which ignites the explosive. The casing is preferably scored to form a series of rectangles which will break into relatively small pieces when the explosive detonates. 
     The propulsion system contained within case  12  is often referred to as a “high-low” system. While a detailed discussion of this system is beyond the scope of this disclosure, a brief description may aid the reader&#39;s understanding of the environment in which the present invention operates. The “high” part of the system refers to high pressure chamber  18 . This chamber is often created by the insertion of a metallic case filled with propellant into base  16 . The open end of the metallic case is closed by burst diaphragm  22 . A primer is contained in the opposite end. 
     A mechanical striker is used to detonate this primer which then causes the propellant within the high pressure chamber to ignite. This action ruptures the burst diaphragm. The expanding propellant gases are then metered through nozzle  24  into low pressure chamber  20 . These relatively low pressure gases act against the aft end of aft closure  38 , thereby propelling the projectile down the firing weapon&#39;s bore. For a more detailed discussion of the propulsion system of the M-433, the reader may wish to review U.S. Pat. No. 7,004,074 to Van Stratum (2006), which is hereby expressly incorporated by reference. 
     A detailed description of the fuse assembly is likewise beyond the scope of this disclosure. However, a fuse assembly typically contains a number of safety features designed to prevent accidental detonation. For example, in some embodiments, the fuse can only be armed when the projectile first experiences a violent forward acceleration followed by a rotation at a minimum rotational velocity. The presence of these two cues indicates that the projectile has been intentionally and successfully fired from a weapon. The fuse assembly will then arm itself during flight. Once armed, any sudden deceleration (such as the projectile impacting a surface) will ignite spitback detonator  32  and explode the grenade. 
     A typical fuse assembly is the M-550 fuse used by the U.S. Army. A discussion of the details of the fuse assembly is beyond the scope of this disclosure. However, the reader wishing to know these details is referred to U.S. Pat. No. 5,081,929 to Mertens (1992). 
     The assembly shown in  FIGS. 1 and 2  functions very well.  FIG. 3  shows projectile  14  flying toward a target.  FIG. 4  shows the projectile striking a target and detonating. Target surface  42  is in this example a reinforced piece of concrete (a hard target). The explosion throws shrapnel  40  in all directions away from the point of impact.  FIG. 5  shows the result, with void  44  being blown into target surface  42 . The projectile is primarily intended as an anti-personnel weapon, and the wide dispersal of shrapnel is obviously effective in this regard. 
       FIG. 6  shows an idealized depiction of the detonation of explosive  34 . Explosive pressure is generally emitted in a direction normal to the surface of the volume of explosive. As the explosive volume depicted is cylindrical, it will emit lateral pressure wave  50  (roughly in the shape of an expanding cylinder), forward pressure wave  46 , and rearward pressure wave  48 . The shape of these pressure waves determine in large part how shrapnel created by the explosion will fly. 
     It has long been known to use a 40 mm grenade as a door breaching round. However, it is often not optimal in this role. In anti-insurgency operations, soldiers must often penetrate occupied buildings. In many instances, it is not known whether the occupants are hostile. However—hostile or not—the occupants will not voluntarily open the door. Thus, the door mush be breached. 
       FIGS. 7 and 8  shows the use of a prior art 40 mm grenade round in this role. In  FIG. 7 , projectile  14  impacts door  52  at a significant velocity (typically about 70 meters per second). Ogive  28  knocks breach 54 into the face of the door. The sudden deceleration ignites the fuse assembly, so spitback detonator  32  ignites the explosive.  FIG. 8  shows the result. The expanding pressure waves from the exploding projectile destroy the door and explosion  58  sends flying debris  56  into the occupied structure. Persons within the structure may be injured or killed. 
     Thus, while the prior art 40 mm grenade round is effective in breaching doors, it may produce unwanted collateral damage. A system which can breach the door without throwing shrapnel into an occupied structure would be preferable. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a modified 40 mm grenade round designed to breach doors without throwing a substantial amount of shrapnel into a building&#39;s interior. The modified round includes a standoff device located on its forward end. The standoff device detonates the explosive charge within the projectile before the nose of the projectile actually strikes the target. This early detonation throws a pressure wave again the door&#39;s exterior, forcing the door inward. Shrapnel produced by the detonation remains primarily outside the door. Thus, the modified projectile is able to blow open a door without throwing a significant amount of shrapnel into a building&#39;s interior. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a perspective view, showing a prior art 40 mm grenade round. 
         FIG. 2  is a perspective view with a cutaway, showing internal details of the prior art grenade round. 
         FIG. 3  is a perspective view, showing a prior art projectile in flight. 
         FIG. 4  is a perspective view, showing the detonation of the projectile upon striking the target. 
         FIG. 5  is a perspective view, showing the resulting damage to the target. 
         FIG. 6  is a perspective view, showing the expanding pressure waves caused by the detonation of a cylindrical volume of explosive material. 
         FIG. 7  is an elevation view, showing a prior art projectile striking a door. 
         FIG. 8  is an elevation view, showing a prior art projectile destroying a door. 
         FIG. 9  is an elevation view, showing a projectile made according toe h present invention approaching a door. 
         FIG. 10  is an elevation view, showing the detonation of the projectile of  FIG. 9 . 
         FIG. 11  is a perspective view, showing the addition of a standoff device to the front of a projectile. 
         FIG. 12  is an exploded perspective view, showing details of the standoff device. 
         FIG. 13  is a sectioned elevation view, showing the operation of the standoff device. 
         FIG. 14  is a perspective view, showing a door being blown open by the present invention. 
         FIG. 15  is a perspective view, showing a steel door being blown open by the present invention. 
         FIG. 16  is an exploded perspective view, showing an alternate embodiment of the standoff device. 
         FIG. 17  is a sectioned elevation view, showing the operation of the alternate embodiment of  FIG. 16 . 
     
    
    
     REFERENCE NUMERALS IN THE DRAWINGS 
     
       
         
               
               
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 10 
                 40 mm grenade round 
                 12 
                 case 
               
               
                   
                 14 
                 projectile 
                 16 
                 base 
               
               
                   
                 18 
                 high pressure chamber 
                 20 
                 low pressure chamber 
               
               
                   
                 22 
                 burst diaphragm 
                 24 
                 nozzle 
               
               
                   
                 26 
                 rifling ring 
                 28 
                 ogive 
               
               
                   
                 30 
                 fuse assembly 
                 32 
                 spitback detonator 
               
               
                   
                 34 
                 explosive 
                 36 
                 casing 
               
               
                   
                 38 
                 aft closure 
                 40 
                 shrapnel 
               
               
                   
                 42 
                 target surface 
                 44 
                 void 
               
               
                   
                 46 
                 forward pressure wave 
                 48 
                 rearward pressure wave 
               
               
                   
                 50 
                 lateral pressure wave 
                 52 
                 door 
               
               
                   
                 54 
                 breach 
                 56 
                 flying debris 
               
               
                   
                 58 
                 explosion 
                 60 
                 standoff device 
               
               
                   
                 62 
                 base 
                 64 
                 tube 
               
               
                   
                 66 
                 contactor 
                 67 
                 flange 
               
               
                   
                 68 
                 door frame 
                 70 
                 steel door 
               
               
                   
                 72 
                 steel bar door 
                 74 
                 tip 
               
               
                   
                 76 
                 contactor 
                 78 
                 cannelure 
               
               
                   
                 80 
                 cannelure crimp 
               
               
                   
                   
               
             
          
         
       
     
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 9  shows an elevation view of a projectile  14  made according to the present invention (shown in flight toward a target). The projectile has a central axis of symmetry, about which it spins during flight. The reader will observe that standoff device  60  has been added to the projectile&#39;s forward portion along this central axis. The standoff device contacts door  52  and transmits a sharp deceleration to the projectile, causing it to explode. When compared to the prior art projectile&#39;s detonation upon contact between the ogive and the door, the detonation in the present case can be said to be “early.” The early detonation is advantageous in certain circumstances—as will be seen. 
       FIG. 10  shows the detonation of the projectile by operation of standoff device  60 . Explosion  58  has occurred while the majority of the projectile remains outside the door. The resulting blast pressure wave propels the door inward. Flying debris  56  remains primarily outside the door. Thus, the projectile has created a door-breaching pressure wave without introducing flying debris inside the structure. Further, a significantly improved result has been achieved using only a relatively small modification. 
     The actual structure of the standoff device can assume many forms, and any particular example should not be viewed as limiting. However, the provision of a few examples will aid the reader&#39;s understanding.  FIG. 11  provides one such example. As for the prior art, ogive  12  encloses the projectile&#39;s forward end. Base  62  is connected to ogive  12  by any suitable means. The connection can be made by adhesive, mechanical fasteners, threads, brazing material, or other known means. Base  62  houses tube  64  and contactor  66  (which collectively comprise standoff device  60 ). 
       FIG. 12  shows an exploded view of these components. Tube  64  fits within a hole in base  62 . Contactor  66  fits within the tube&#39;s hollow interior. Tip  74  is positioned to strike ogive  12  when contactor  66  strikes a target surface. 
     The fit of the contactor within the standoff device is preferably configured to minimize the risk of unwanted movement (and consequent premature detonation). The reader will observe that the contactor includes a flange near its forward extreme that laps over the end of the tube. The contactor preferably also includes circumferential or other serrations intended to create sliding resistance between itself and the tube. 
       FIG. 13  shows a sectioned elevation view depicting the operation of the standoff device. In the left view the contactor is in position on ogive  12 . The reader will observe that base  62  has a cavity designed to receive the shape of ogive  12  (The cavity opens downward in the orientation shown in the view to receive the upward facing ogive). Tube  64  fits securely within a corresponding passage provided in the base. The tube can be attached via a press fit, a sliding fit secured with adhesive, a threaded engagement, or some other suitable fastener. Contactor  66  is pressed into the open end of tube  64  until the contactor&#39;s flange  67  comes to rest against the tube&#39;s forward extreme as shown. The reader will observe that tip  74  is separated from ogive  12 . This separation, which is optional, can be used to provide a slight delay in the detonation sequence. 
     In the right hand view of  FIG. 13 , contactor  66  has contacted a target surface and has consequently been propelled toward ogive  12 . The contactor&#39;s flange has been driven into the tube and plastically deformed the tube along its progress. Tip  74  has contacted ogive  12  and imparted a substantial deceleration to the projectile. Those skilled in the art will know that such a substantial deceleration will cause the fuse mechanism to detonate the explosive contained within the warhead. 
     It is instructive to consider the timing effect of the standoff device. At the time of impact, a 40 mm grenade is typically traveling at about 70 meters per second. The standoff device effectively “projects” the nose of the projectile forward a set distance (which is typically less than the overall length of the standoff device owing to the separation of the tip from the ogive, the crush timing of the tube, etc.), thereby creating an “early” detonation. If the effective distance is 3 cm, then a projectile traveling at 70 m/s (7,000 cm/s) will detonate approximately 3/7,000 or 4.3×10 −4  seconds earlier than a prior art projectile. 
     There is of course a delay in the operation of the fuse mechanism and the spitback detonator but—as those skilled in the art will know—the operation of these devices is typically measured in microseconds. The result of the standoff device is the projectile detonating just outside the door instead of detonating as the ogive is actually penetrating the door. 
       FIGS. 14 and 15  show the present invention in operation. In  FIG. 14 , a projectile including a standoff device has been fired at a wooden door  52  within door frame  68 . Explosion  58  has sent a pressure wave against the outward-facing surface of the door, blasting the door inward. Wooden doors and frames typically fail by tearing the striker plate out of the frame or the bolt mechanism out of the door. Neither of these modes is likely to throw flying debris into the structure. The external detonation has breached the door while keeping most—if not all—of the shrapnel outside the structure. 
       FIG. 15  shows the device being used against a steel door  70  in a steel door frame. The projectile has again detonated outside the door. The substantial pressure wave will often warp a steel door and thereby pull its bolt free of the striker assembly. 
       FIG. 15  shows another operational feature. In some installations a steel door is hinged to open inward while a steel bar door  72  (a “burglar bar door”) is hinged to open outward. The properly constructed standoff device causes the projectile to detonate while it is between the doors. The resulting pressure waves blow the interior door inward and the steel bar door outward—thereby simultaneously opening both obstacles. 
     As discussed previously, a variety of different designs could be used for the contactor.  FIG. 16  shows one such alternate embodiment. In this version contactor  76  includes a series of circumferential cannelures  78  (A “cannelure” is a circumferential groove traditionally used to receive a roll crimped deformation of the mouth of a cartridge case, thereby positively locating a projectile within the mouth of a cartridge case). Tube  64  is a simple hollow cylinder, preferably made of a malleable material such as brass or aluminum. 
       FIG. 17  shows a sectioned elevation view of this alternate embodiment installed on a projectile. The base is attached to the ogive as in the prior embodiment. The tube is then held within the base. However, contactor  76  is retained within tube  64  by crimping at least a portion of the tube into one of the cannelures in the contactor. This crimp forms cannelure crimp  80 —a circumferential interference between the contactor and the tube. 
     By studying  FIG. 17  the reader will quickly appreciate that this design allows for variation in the offset distance between tip  74  and ogive  12 . By selecting which cannelure groove the tube is crimped into, one may easily select this offset distance. The variation of the offset distance varies the timing of the detonation. This, in turn, allows a user to select a greater or lesser standoff distance for the detonation. This would not typically be done in the field, but a variety of standoffs could be provided with various color or other coding to inform the soldier of the standoff distance set for a particular device. A different standoff distance or configuration could be optimized for different door types. One type might be suitable for steel doors while another might be suitable for wooden doors. 
     The illustrated examples of the standoff device have shown a separate assembly attached to an existing ogive. This need not always be the case. A modified ogive could be fashioned which would incorporate the base as an integral piece. The tube and contactor could also be integrated as a unified piece with each other and possibly the ogive. 
     However, it is preferable to provide some type of telescoping assembly in the standoff device. This allows the standoff device to detonate the projectile without significantly penetrating the target surface. A completely rigid standoff device—as an example—may penetrate too far into a thin wooden door before detonating. 
     Finally, the ogive may be modified to allow the selective addition of a standoff device in the field. As an example, the ogive could have a hole in its forward portion designed to receive the tube and contactor. This hole could include female threads sized to receive male threads on the tube. The ogive could also include a threaded boss or other convenient attachment device. 
     The preceding description contains significant detail, but it should not be construed as limiting the scope of the invention but rather as providing illustrations of the preferred embodiments of the invention. As an example, the physical characteristics of the base could be modified substantially while still providing the basic function of attaching the standoff device to the ogive. Thus, the scope of the invention should be fixed by the following claims, rather than by the examples given.