Patent Grant
10066916
The invention relates in general to explosive ordnance disposal (EOD) and in particular to projectiles for EOD disruptors, including but not limited to percussion activated non-electric (PAN) disruptors and electrically initiated EOD disruptors.
Some known improvised explosive device (IED) threats and newly emerging IED threats use steel-cased devices containing thermal and/or impact sensitive propellants or thermal or impact sensitive explosives. Currently used render safe procedures (RSPs) carried out with gun-type EOD disruptors use high velocity steel or other metal or metal composite projectiles moving in excess of 2000 fps to vent hard cased IEDs. The unexpected consequences of this approach are the tremendous pressures and shock waves that are produced. For example, steel projectiles that hit steel targets have matched shock impedances and thus efficiently propagate shock waves. Such shock waves can compress the explosives that fill the IED. The explosives are pressed against the side of the casing in the projectile impact zone.
The explosives' compression occurs quickly and adiabatic conditions are created. For example, after projectile impact, black powder inside an IED can be compressed and heated to ignition, resulting in an IED exploding and fragmenting. In the case of double and triple-based smokeless powder, the nitroglycerin-containing propellant detonates immediately after the projectile hits the IED. The RSP creates an explosion that is far more violent and lethal than if the IED simply functioned as designed. Most IEDs are initiated through pyrotechnic fuzes or electric matches. Of particular concern are steel capped pipe bombs, steel plugged elbow pipe bombs, and improvised grenades.
A conventional technology may pierce relatively thin-walled steel containers, for example, a steel drum or a steel ammo box, without initiating the explosive therein. Even so, such conventional technology cannot pierce, for example, 2 inch diameter schedule 40 steel cased pipe bombs. A need exists for EOD projectiles that can penetrate a relatively thick steel case of an explosive device without detonating the explosives in the device.
One aspect of the invention is an apparatus that includes an EOD disruptor with a barrel. A blank cartridge may be loaded in the EOD disruptor. A water column may be disposed in the barrel in front of the blank cartridge. A water plug may be disposed in front of the water column. The apparatus may include a muzzle-loaded projectile having a central longitudinal axis and disposed in front of the water plug. The projectile includes a shaft portion at least partially disposed in the barrel and a front portion disposed outside of the barrel. A ratio of the length of the shaft portion to the inner barrel diameter may be in a range of about two to about fifty. The projectile may have a weight from about four ounces to about two pounds.
In some embodiments, the entire shaft portion of the projectile may be disposed in the barrel. In other embodiments, the amount of the shaft portion that is disposed in the barrel is variable.
Various embodiments of the projectile include a shaft portion with a sub-caliber diameter. In these embodiments, the projectile may include least one bushing slidably mounted on the shaft portion.
A restraint system may be included for limiting the distance travelled by the projectile.
Another aspect of the invention is a method that includes providing the novel apparatus and firing the projectile from the EOD disruptor with a muzzle velocity of less than about 1000 feet per second. Before firing, the shaft portion may be situated fully or partly in the barrel.
The invention will be better understood, and further objects, features, and advantages thereof will become more apparent from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings.
In the drawings, which are not necessarily to scale, like or corresponding parts are denoted by like or corresponding reference numerals.
Projectile 16 may be made of, for example, steel, tungsten, metal alloys, and composites. Different portions of the projectile 16 may be made of different materials. The projectile 16 includes a generally cylindrical shaft portion 30 at least partially disposed in the barrel 12 and a front portion 18 disposed outside of the barrel 12. In the embodiment shown, the front portion 18 includes a beveled cutting edge 38, such that the projectile 16 resembles a chisel. In other exemplary embodiments, front portion 18 may be a forked blade, a blunt cylindrical end, an ogive shape, a pyramidal shape with up to four cutting edges, or a shape with rows of pyramidal shaped teeth, for example. A forked blade is effective at cable, wire and detonation cord cutting. A bushing tool with pyramidal shaped teeth is effective at removing the external end caps from pipe bombs. Projectile 16 may be coated with a non-sparking and friction reducing material, for example, cutting oil or Cerakote™. Projectile 16 may also be placed in a plastic sheath such as a sabot-style covering to enable the use of reduced diameter projectile shafts in the barrel.
In the embodiment shown in
The projectile mass distribution may be non-uniform. The majority of the mass may be placed on the head of the projectile such that the center of pressure and gravity are at the same location. This mass distribution creates a center of mass front of center, which allows for stable flight for projectiles ejected from smooth-bored barrels. The projectile 16 may be symmetric about its central longitudinal axis X (
In the embodiment shown in
In the embodiment shown, four bushings 46 are shown, but more or fewer bushings 46 may be used. Bushings 46 may be made of, for example, steel or tungsten. In the embodiment shown, bushings 46 may have an outside diameter of about 0.70 inches. The length of each bushing 46 may be in a range of about 0.5 inches to about 1.5 inches. A combined length of bushings 46 may be in a range of about 1 inch to about 9 inches.
The front portion 44 of projectile 40 may be disposed outside of the barrel 12. In the embodiment shown, the front portion 44 includes a beveled cutting edge 38. In other embodiments, front portion 44 may be a forked blade, a blunt cylindrical end, an ogive shape, a pyramidal shape with up to four cutting edges, or a shape having rows of pyramidal shaped teeth, for example. In some embodiments, the shaft portion 42 may have a length of about four inches to about eighteen inches. More particularly, the shaft portion 42 may have a length of about eight to fourteen inches. The ratio of the length of shaft portion 42 to the inner barrel diameter may be greater than 2 and may be as high as 50. In some embodiments, the projectile 40 may have a weight from about four ounces to about two pounds. More particularly, the projectile 40 may have a weight from about twelve ounces to about twenty-four ounces.
When projectile 40 is fired from disruptor 10, the bushings 46 are pushed rearward on shaft portion 42. When projectile 40 impacts a target, the bushings 46 slide forward and provide a second series of pressure waves and thus increase the time the projectile is pushing through the target barrier. This additional impulse allows one to reduce the strength of the blank cartridge 22 to thereby reduce the recoil of the disruptor 10. Sometimes, the disruptor recoil may be too great for deploying the disruptor with a robot. If the disruptor recoil is decreased, robotic deployment may be possible.
Projectiles 16, 40 may be fired from disruptor 10, or any other gun-type EOD disruptor having an appropriately pressure rated breech, with a muzzle velocity of less than about 1000 feet per second. More particularly, the muzzle velocity may be less than about 500 feet per second.
To limit the down range hazard of projectiles 16, 40, a restraint system may be employed, such as a tether 52 (
Test Results
Testing has verified that lowering the velocity of a PAN projectile and increasing its mass and length can dramatically reduce the likelihood of ignition of IEDs and eliminate detonation of smokeless powder inside IEDs. A small decrease in velocity results in a much larger decrease in shock pressure because the pressure is proportional to the square of the projectile velocity.
For capped pipe bombs, a conventional defeat method uses the frangible AVON projectile (1 ounce of steel shot, 2,000 fps). Capped pipe bombs also have been defeated using the Remington Nitroturkey™ shot shell (2 ounces of lead shot, 1300 fps). The Nitroturkey™ shot shell was not effective at defeating plugged elbow pipe bombs. Ignition and fragmentation resulted. It was believed that the projectile needed to have an even lower velocity to avoid shock conditions and compressive heating, which occur when the pressure wave moves faster than the speed of sound in the impacted material.
The inventive projectile manipulates the projectile momentum transfer (impulse) to cut through the pipe elbow and knock out the plug. The impact force needs to be greater than the yield strength of the steel case. The projectile velocity was lowered to approximately 300 fps or less. The lower velocity reduced the impact pressure and did not produce shock waves, yet the projectile penetrated the elbow and knocked out the plug. Compared to a conventional steel slug projectile, the mass of the inventive test projectile was increased about 24 times. The steel slug projectile is used in the standard RSP. Tests showed that the steel slug failed 90% of the time.
The duration of collision of the projectile also was increased. The duration is proportional to 2L/C, where L is the projectile length and C is the speed of sound in the projectile. In the test projectile, the duration was increased 10 times compared to the steel slug projectile. To emphasize the importance of impact duration, theoretically, a 300 fps projectile of about 1.5 pounds having the length of a conventional steel slug would not rupture a plugged elbow. The dramatically increased length of the shaft portion of the novel projectile was proven to be ideal for steel pipe bombs and nipture and defeat of other kinds of IEDs.
The shaft length and projectile velocity are not mutually exclusive. It has been demonstrated that the velocity of the projectile is approximately proportional to the projectile depth in the barrel. Using a shaft portion approximately ten inches long seated the novel projectile deep enough into the disruptor barrel to create the required muzzle velocity of 300 fps.
Projectile tip profile also has an effect on penetration. Decreasing the cross sectional area of a projectile tip results in greater projectile penetration through a barrier. While a blade shaped projectile head increases the impact pressure, it has the benefit of reducing the material being compressed at the interaction region. The barrier yields quickly so the required impact duration is reduced and less energy is transformed into heat. The test projectile used a 3″ wide blade (chisel head) to defeat 2″ diameter steel capped and elbow plugged pipe bombs. Two inch diameter pipe fittings are commonly used in IEDs in the United States.
Because of the large length of the shaft portion of the novel projectile, the velocity of the projectile may be adjusted in a continuum of velocities by changing how deeply seated the shaft portion is placed in the barrel. This adjustment is not possible with a conventional short shaft, chisel head projectile.
The novel projectile may include a water column to its rear. The water column has been shown to double the energy output compared to a projectile that has an air gap between the back of the projectile and the blank cartridge. The water creates a hydraulic seal, which decreases propulsion gas blow-by and increases the propulsion gas pressure that drives the projectile forward. A secondary benefit of the water column is a fluid jet that follows the projectile and suppresses thermal effects on the target.
There are four conventional blank 12 gauge cartridges of different explosive strengths in common use: enhanced, high velocity, medium velocity and low velocity. Other commercial specialty blank cartridges are available. This variety of cartridges provides further flexibility in projectile velocity and impact pressure. Thinner skinned targets can be ruptured more gently and thus reduce the risk of ignition. Other specialty blank cartridges with different powder loads and type can be constructed using standard reloading techniques. These blank cartridges can customize the pressure time history of a projectile.
Any numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of significant digits and by applying ordinary rounding.
The invention described herein may be manufactured and used by or for the Government of the United States of America for Governmental purposes without the payment of any royalties thereon or therefor.
| Number | Name | Date | Kind |
|---|---|---|---|
| 2491516 | Piggot | Dec 1949 | A |
| 4046055 | McDanolds | Sep 1977 | A |
| 6439127 | Cherry | Aug 2002 | B1 |
| 6644166 | Alexander | Nov 2003 | B2 |
| 8276495 | Chiu | Oct 2012 | B1 |
| 9404718 | Shaver | Aug 2016 | B1 |
| 20110061521 | Gardner | Mar 2011 | A1 |
| Number | Date | Country |
|---|---|---|
| 2083894 | Apr 1996 | ES |
| 2083894 | Mar 1982 | GB |
| Entry |
|---|
| AB Precision (Poole) Ltd., Explosive Ordnance Disposal, ABL 900, Jan. 2009, United Kingdom. |
| AB Precision (Poole)Ltd., Explosive Ordnance Disposal, ABL 2000, Jan. 2009, United Kingdom. |
| Nexus Defense, ABL 3000 Recoiless Disrupter & De-Armer, Publication Date unknown, United Kingdom, accessed on Feb. 4, 2018 at http://www.nexus-defence.com. |
