Patent Application
20120216698
Not Applicable.
Not Applicable
1. Field of the Invention
This invention relates to the field of projectile delivery systems. More specifically, the invention comprises an explosive projectile designed to breach a door while producing very little shrapnel.
2. Description of the Related Art
Although the components of the present invention can be applied to many different types of projectiles, they were primarily developed as a component of existing 40 mm grenade weapons (such as the U.S. Army's M-433). While those skilled in the art will be familiar with such weapons, a brief description may nevertheless be helpful.
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's bore. Rifling ring 26 engages internal rifling on the firing weapon'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 profile 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. Thus, it may assume a wide variety of shapes. The ogive generally contains the arming and detonating mechanisms. The volume between the ogive and the rifling ring typically contains the explosive.
Explosive 34 is contained within casing 36. Fuse assembly 30 is contained within ogive. The fuse assembly activates spitback detonator 32 when the projectile strikes a target object (assuming it has been appropriately armed). The spitback detonator then initiates explosive 34. Casing 36 is typically 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'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 initiate. 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'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 initiate 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
It has long been known to use a 40 mm grenade as a door breaching round. However, it is 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 must be breached.
In addition, debris from the door and the casing of the projectile itself may be thrown back toward the shooter. This fact forces the shooter to stand back a considerable distance (such as 30 meters). It is more desirable to station the soldier or soldiers preparing to enter a structure much closer to the door, so that there will be little delay between the detonation of the grenade and their entry.
Thus, while the prior art 40 mm grenade, round is effective in breaching doors, it may produce unwanted collateral damage and may unduly delay the entry of a security team into a structure. A system which can breach the door without throwing significant shrapnel would therefore be preferable.
The present invention is a modified 40 mm grenade round designed to breach doors without throwing a significant amount of shrapnel into a building's interior or back toward the shooter. The modified round includes a forward extension on the ogive. The extension is rigidly connected to a thrust column which transmits an impact load directly from the ogive's nose cap to the striker on the fuse assembly. This configuration detonates the explosive charge within the projectile while the explosive is still well outside the door. This early detonation throws a pressure wave again the door's exterior, forcing the door inward.
The projectile includes primarily plastic components which fracture into light and small debris when the explosive detonates. The projectile preferably also includes bore-riding cylindrical surfaces in the body and the ogive. These surfaces minimize balloting and resulting off-axis wobble as the projectile exits the muzzle of a weapon.
The round is made to be fired from a rifled bore. Propulsion assembly 13 remains in the breech end of the bore when the round is fired. Detonation assembly 74 and body 76 together form a projectile which flies downrange as a unit. Acceleration of the projectile is accomplished using the same “high-low” pressure system as for the prior art. The propellant within high pressure chamber 18 is initiated. Burst diaphragm 22 then ruptures and meters the expanding propellant gas into low pressure chamber 20 (which is the void between the aft end of body 76 and base 16). Body 76 contains explosive 34. The explosive is initiated by fuse assembly 30, which will be explained in more detail subsequently.
Female thread 90 is provided on the forward portion of cylindrical side wall 82. This feature is used to join the body to detonation assembly 74. Rifling ring 26 is provided on the aft end of body 76. The body may be made from a relatively soft material such as reinforced plastic. The rifling ring is intended to engage the grooves and lands in the firing bore so that the projectile may be rotationally accelerated as it travels down the bore. It is therefore preferable to make the rifling ring out of tougher material—with aluminum being a good choice.
Those skilled in the art will know that a rifled bore is often defined by two distinct diameters. First is the “bore diameter” or “land diameter.” Second is the “groove diameter,” which is the diameter of a circle passing through the deepest part of the rifling grooves. The bore is defined by a set of “lands” (the protruding areas between the grooves). While the lands are often thought of as having considerably ore surface area than the grooves, this is not always the case. In fact, many modern rifled bores have more groove area than land area.
Rifling ring 26 includes one or more groove engaging protrusions which have a diameter greater than the land diameter of the rifled bore. The rifling ring also includes lip receiver 88, which is configured to receive lip 80 on case 12 in a snap-fit configuration.
Aft closure 84 preferably includes aft pocket 86, which serves several functions. Turning briefly back to
Spitback detonator 32 is attached to the aft end of fuse assembly 30. The fuse assembly is in reality a complex mechanism which is only represented in a conceptual form in
The fuse assembly typically contains a set-back safety device and a rotation safety device. Both these safety devices must be in the “fire” position in order for the striker to produce the detonation of spitback detonator 32. The set-back safety device must receive a sharp acceleration in the forward direction in order to switch from a “safe” configuration to a “fire” configuration. This occurs when the projectile is fired from the rifled bore.
The rotation safety device is switched from a “safe” position to a “fire” position when the projectile rapidly rotates through a defined number of rotations. This occurs when the rifling in the bore of the launching weapon rotationally accelerates the projectile to the spin rate it will experience in flight. The rotation safety device generally requires multiple rotations so that the weapon will have an “arming distance”—meaning that the fuse assembly cannot be fired until it has traveled a specific distance.
For prior art rounds, the arming distance is generally 14 m to 28 m. This requirement means that the safety devices are set so that no specific round out of a large sample will be armed before it has traveled 14 m and every specific round out of a large sample will be armed after it has traveled 28 m. Once the safety mechanisms are armed (in the “fire” position) a blow to striker 100 will actuate the fuse assembly. Spitback detonator 32 will then be fired and the explosive within the projectile will be initiated.
Standoff ogive 118 includes nose cap 104. The forward tip of the nose cap extends a significant distance beyond what would be the tip of a conventional ogive. This distance is denoted as extension 114.
The outer wall of standoff ogive 118 has three distinct regions in the particular embodiment shown. Cylindrical side wall 108 exists in the aft region. The thicker wall of nose cap 104 exists in the forward region. Sloping side wall 106 joins these two regions together into a unified whole. Of course, the separate regions may be formed by multiple independent parts linked together. In the embodiment shown, however, the three regions are formed as one integral piece.
A significant design feature of the present invention is the rapid transmission of impact forces experienced by nose cap 104 to striker 100. Thrust column 102 is provided for this purpose. While the thrust column may assume many geometric forms, it is important that it be relatively stiff.
In the embodiment shown, the thrust column is a hollow cylinder that is integrally molded with the balance of the standoff ogive. Graphite reinforced NYLON may be used for the standoff ogive and this provides sufficient stiffness. In other embodiments, a relatively soft material could be used for the nose cap and side walls, with a stiff metal cylinder being used for thrust column 102. Whatever configuration is used, the forward portion of the thrust column is connected to the nose cap while the aft portion rests against striker 100. Since the striker in the embodiment of
In the embodiments shown, body 76 is joined to detonation assembly 74 by engaging male thread 96 (on the aft end of fuse assembly 30) and female thread 90 on the forward end of body 76. Uniting these two subassemblies creates a projectile. The projectile must be joined to the propulsion assembly so that they remain an integral unit up until the time when the grenade round is fired.
It is preferable to mold standoff ogive 118, body 76, and case 12 as plastic components. The use of plastic allows novel joining techniques. The reader will recall from
Material selection is significant to the advantages provided by the present invention. Returning now to
Looking specifically at
In the prior art, the components surrounding the explosive tend to be conductive metal. In the present invention, however, the components tend to be non-conductive plastics. One way to resolve this problem is to coat the graphite reinforcing fibers in the plastic with conductive nickel. Another approach is to apply a thin conductive layer (such as deposited nickel) to the interior surface of the plastic components. Either approach provides sufficient conductivity to eliminate the problem of electrostatic discharges.
The use of plastic components throughout the projectile greatly reduces the production of harmful shrapnel upon detonation. The metal components of the fuse assembly tend to fly forward toward the door, where they are broken into even smaller particles. The metal of the rifling ring breaks into aluminum fragments having high surface area and low mass. These decelerate rapidly. The remaining plastic fragments are very small and produce little damage. As a result, a soldier firing the breaching projectile at a door may stand as close as 10 m. The arming range of the fuse assembly should be adjusted to 9-14 m (as opposed to 14-28 m for the prior art).
The use of plastic components in combination with appropriate geometry also serves to reduce “balloting” as the projectile accelerates down the bore and out the muzzle. “Balloting” refers to a precessing yaw of a projectile's centerline as it travels down the bore and exits the muzzle.
Ideally, the projectile's centerline remains perfectly concentric with the centerline of the rifled bore. In prior art grenade rounds, only a portion of the projectile's external surface engages the bore of the firing weapon. A forward “bore riding” ring is usually provided along with an aft rifling engaging ring. Balloting could be largely eliminated by providing the projectile with a smooth cylindrical surface sized to closely slide within the land diameter of the rifled bore (the “bore diameter”). However, many grenade launching weapons use soft metal barrels (such as thin walled steel or aluminum tubing). A close sliding fit with a metal projectile will quickly wear out the bore in such weapons.
The present invention uses much softer plastic materials, however. Even a soft bore material can endure many firings of a soft plastic projectile without significant degradation. Geometry is preferably included to minimize balloting.
Turning now to
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 shape of the standoff's ogive's side wall could be modified while still providing the basis function of the present invention. Many other alterations will occur to those skilled in the art. Thus, the scope of the invention should be fixed by the following claims, rather than by the examples given.
This application is a continuation-in-part of U.S. application Ser. No. 12/657,405. The parent application was filed on Jan. 19, 2010. It lists the same inventor and remains pending as of the date of filing of the present application.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12657405 | Jan 2010 | US |
| Child | 13070984 | US |
