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Mk 258 Armor Piercing, Fin Stabilized, Discarding Sabot-Tracer (APFSDS-T)
Anti-Mine Projectile Hydroballistic Ammo 30mm Ammunition

The 30mm Mk 44 gun is capable of using the Mk 258 Mod 1 armor-piercing fin-stabilized discarding sabot tracer (APFSDS-T) round. The projectile, intended for use in the US Navy's Rapid Airborne Mine Clearance System (RAMICS), is stable during air flight, successfully penetrates the water's surface, supercavitating while in the water, to greatly reduce drag and improve underwater flight performance. RAMICS was designed to be capable of neutralizing near-surface and surface-moored mines in the shallow water zone (40 to 300 feet total water depth) and the deepwater zone (greater than 300 feet total water depth).

Supercavitating projectiles are characterized by substantially reduced hydrodynamic drag with respect to fully wetted underwater vehicles. Drag is localized at the nose of the vehicle, where a cavitator generates a cavity that completely envelops the body. This causes the center of pressure to be always ahead of the center of mass, thus violating a fundamental principle of hydrodynamic stability. This unique loading configuration, the complex and non-linear nature of the interaction forces between vehicle and cavity, and the unsteady behavior of the cavity itself make the control and maneuvering of supercavitating vehicles particularly challenging.

Development of penetrating projectiles used in anti-armor applications addressed numerous technological difficulties in order to produce effective weapons. The basic requirements of a long-rod penetrator included the use of high density projectiles having a long length-to-diameter ratio and having very high impact velocities. Then available projectiles were generally used for maximum target penetration of a hardened structure. The invention adapts long-rod penetrators with the capability of traveling both in air and water where the object is to achieve low-drag water penetration for the purpose of delivering high kinetic energy to underwater targets. This required that the hydroballistic projectile maintain stability and low drag both in air and water so that sufficient kinetic energy can be delivered to the underwater target to assure its destruction.

Existing projectiles did not exhibit the capability to travel in both air and water and deliver high kinetic energy to defeat targets at any significant depth below the water surface. An operational need existed for a projectile to have the capability of launch above the water surface and provide effective water travel after impact with the water surface.

The supercavitating water entry projectile has aft mounted empennage which was designed to provide stabilization in both air and water and a supercavitating nose section. The projectile is a subcaliber gun launched munition using an appropriate sabot assembly to provide full caliber integrity. The projectile has circumferential grooves around its center section to match grooves in the sabot assembly. A key feature in the invention is the size and shape of the nose section. The projectile has a novel high strength extended blunt nose section followed by a truncated conical section which angles towards the body of the projectile in the range of five degrees. During underwater trajectory, the entire projectile is contained within the cavitation bubble formed by the blunt nose tip. The projectile's empennage, which provides both aerodynamic and hydrodynamic stability, fits within the bore of the weapon.

The 30mm Anti-Mine Projectile (AMP), was a growth evolution of the proven 20mm RAMICS ATD supercavitating projectile, and was designed to be compatible with the family of 30 mm x 173 ammunition used on the Mk 44/Bushmaster II gun system. This system was already expected to be deployed in substantial numbers on the Marine Corps' Advanced Amphibious Assault Vehicle (AAAV) scheduled to enter service between 2000 and 2010. The system was also expected to find use in a number of marine and airborne applications with US and allied forces.

The munition offered long underwater lethal range (140'+) and single hit kill capability against a wide range of insensitive mine types. Prompt deflagration of the mine's warhead, independent of any fuse or trigger function, provides immediate bomb damage assessment (BDA) to the warfighters in the form of a visible surface plume.

The lethality of the round gives a simple look, shoot, kill capability to the helicopter crew enabling them to maintain a rapid tempo of operations and maximizing the tactical effectiveness of every mission while minimizing exposure to hostile forces.

C Tech currently offers supercavitating round designs in 50 caliber, 20mm, and 30mm sizes, and can quickly and cost effectively create a point design and prototypes suited to specific applications.

The Mk 258 Mod 1 APFSDS-T is capable of being fired from the 30mm Mk 44 Automatic Gun. The ammunition was required to be capable of entering the water at an angle of 60 degrees from the horizontal and continue in water to a range of 75 feet. The velocity after traveling 75 feet in water had to be greater than 3000 feet per second. The kinetic energy of the projectile after 75 feet of water travel needed to be greater than 46,000 foot-pounds. The ammunition also needed to be suitable for naval rotary wing applications and meet safety requirements needed for U.S. Navy Weapon Systems Explosive Safety Review Board (WSESRB) certification. The ammunition was required to meet standard U.S. Navy safety and performance cartridge characteristics (i.e. chamber pressure, primer sensitivity, action time, cartridge integrity, etc.).

In April 2004 the US Government announced plans to procure on a sole source basis from Nammo AS, Raufoss, Norway the Mk 258 Mod 1, 30mm x 173mm cartridge. This contract action was for a basic quantity of 5,000/ea rounds (rds) with one option of 10,000/ea rds and another option for 15,000/ea rds. The contract also required data. The US Government required delivery of the basic contract quantity along the following timeline: 500 rounds within 120 days of order with delivery of the remainder within 365 days after the effective date of the contract.




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