M230 chain gun

The Hughes M230 Chain Gun is a 30 mm, single-barrel automatic cannon developed by Hughes and now manufactured by Alliant Techsystems. It is an electrically operated chain gun, a weapon that uses external electrical power (as opposed to recoil or expanding gas generated by the firing cartridge) to cycle the weapon between shots.

Development
In 1972 Hughes Helicopters began a company-funded research effort to design a single machine gun to fire the U.S. Army's M50 20 mm round. By April 1973, the program had fired test rounds in more powerful 30mm WECOM linked ammunition, from a prototype (A model). In January 1975 a model "C" was added, a linkless version for the proposed Advanced Attack Helicopter YAH-64; the helicopter was eventually adopted as the AH-64 Apache, with the model C as standard armament. The linked ammunition version was intended for the AH-1S Cobra, but was later dropped.

Apache and DAP mounts
The M230 Chain Gun is the Area Weapon System on the AH-64 Apache attack helicopter and is also used on the MH-60L Direct Action Penetrator (DAP). The M230 is mounted on the chain gun turret. It uses a 2 hp electric motor to fire 30 mm linkless ammunition at a rate of 625 (±25) rounds per minute. The gun requires a spool-up time of 0.2 seconds to achieve this rate of fire. The practical rate of fire is about 300 rounds per minute with a 10 minute cooling period as the gun is air cooled. The gun has a positive cook-off safety for open bolt clearing, and double ram prevention. Spent casings are ejected overboard through the bottom of the gun.

The mount on the AH-64 uses secondary hydraulics to move the gun. Elevation is provided via a single hydraulic actuator located on the gun's centerline just forward of the pivot point. The gun is spring-loaded to return to its centerline stowed position with the barrel angled up about eleven degrees in the event of a loss of hydraulic power. This allows the gun, which is mounted below the copilot station, to collapse cleanly into its designed space between the pilot stations in the event of a hard landing. This prevents the gun from entering the pilots stations and becoming a hazard.

The Apache is capable of carrying up to 1,200 rounds for the gun in a device known as the flat pack. However, utilization by the US Army of a special internal fuel tank, the Robertson IAFS (known as the Robby Tank to the crews), reduces this capacity to 300 rounds. The ammunition is loaded into the AH-64D Longbow Apache by armament personnel using an aircraft-mounted motorized loader and special ammunition handling tray. The AH-64A requires specialized ground support equipment for loading.

The M230 is capable of firing the ADEN/DEFA 30×113 rounds, however, the Lightweight 30 mm rounds (M788/M789/M799) used in the M230 are constructed with a light alloy as opposed to brass or steel casings to save weight and are in use with the US Army. The M230 rounds are not backwards compatible with weapons designed for the ADEN or DEFA rounds. The M788 rounds can be distinguished by the blue band near the nose, the M789 by a yellow stripe atop a black band and the M788 a red stripe atop a yellow band. The M799 HEI round is not used by the US Army due to the danger of a round exploding in the gun barrel. General Dynamics Ordnance and Tactical Systems, a business unit of General Dynamics (NYSE: GD), has been awarded a contract for the production and delivery of 30mm M789 High Explosive Dual Purpose (HEDP) ammunition cartridges by the U.S. Army Contracting Command. The 30mm M789 HEDP is the primary tactical round of the Apache AH-64 helicopter, widely used in current combat operations. The Apache’s ability to provide accurate air support with minimal collateral damage led to increased use and volume demands for M789 ammunition.

The M789 is typically used in the M230. Each round contains 21.5 g of explosive charge sealed in a shaped-charge liner. The liner collapses into an armor-piercing jet of metal that is capable of penetrating more than 2 inches of RHA. Additionally, the shell is also designed to fragment upon impact. The lethal radius against unprotected, standing targets is about 10 ft under optimum conditions. The M789 requires about 2 seconds to travel 1000 m. However, as the shell slows down, it takes over 12 seconds to cover 3000 m.

M230LF and MAWS
The M230LF, offered by ATK is a more capable version of the Apache autocannon. Features include an anti-hangfire system, a delinking feeder that exploits linked ammunition, and an extended-length barrel, which results in greater muzzle velocity and hitting power from the same M789 HEDP and NATO standard 30mm ADEN/DEFA projectiles. The rate of fire is reduced to 200/minute and overall length increased to 85.87 in. The chain gun can be installed in an enclosed turret on patrol boats and ground vehicles.

The MAWS (Modular Advanced Weapon System) lightweight gun system, developed in partnership with the U.S. Navy, utilizes a remotely operated M230LF in an open mount. It is controlled by a Remote Operator's Console (ROC)—with either dual grips or a joystick—from a touch panel display and extended day color TV.

Aircraft use

 * Boeing AH-64 Apache
 * AgustaWestland Apache
 * Sikorsky MH-60L Direct Action Penetrator (DAP)