M900 105mm APFSDS-T
The M900 Depleted Uranium APFSDS-T [Armor Piercing Fin Stabilized Discarding Sabot - Tracer] cartridge is the primary anti-armor 105mm tank ammunition in service with the United States Army and Marine Corps. This fourth-generation kinetic energy projectile is capable of penetrating the frontal slope of fielded adversary armor systems. The penetrator and sabot design provides excellent accuracy at all combat ranges. This cartridge is compatible with the US M-1, M-60, and M-48 series tanks emplying the 105mm M-68 cannon.
The current KE cartridge, the M900 Armor Piercing, Fin Stabilized, Discarding Sabot with Tracer (APFSDS-T), will provide the Stryker MGS with the capability to destroy a variety of light skinned and armored vehicles (through the T-62 tank) in a self-defense role. The cartridge is currently in inventory and was originally developed and procured for the M1 Abrams tank. This round was type-classified in 1989.
The electrically initiated primer ignites the propelling charge and tracer. Gases produced by the burning propellant propel the projectile from the gun. The tracer burns for a minimum of 2.5 seconds. The sabot is discarded after leaving the muzzle of the weapon, as a result of setback, centrifugal, and air pressure forces. The solid core of the projectile continues to the target.
In order that only minimal spin is imparted to the projectile when the obturator engages the gun tube rifling, the plastic seal under the obturator produces approximately 80% slippage. Target penetration is effected strictly by the high kinetic energy of the subprojectile impacting the target.
The cartridge is equipped with a depleted uranium penetrator section designed for a muzzle velocity of 1,500 meters per second. The M-900 is made up of a steel case and savoy, depleted uranium penetrator rod, M43 propellant, and a fuse.
The M900 is authorized for use in M1 tanks only. Firing the M900 from any other 105mm tank system may result in failure of the gun mount. Firing in unauthorized gun mounts will result in failure of the recoil mechanism hydraulic seals.
Do not fire the M900 from 105mm, M68 series cannon equipped with breeches having serial numbers lower than 4804. These breeches can fail catastrophically without warning. Initial quantities may be stenciled with a note indicating a cutoff point at serial number 6000. This number should no longer be considered valid.
Do not fire the M900 cartridges where the projectile is loose within the case; i.e., rotating, wobbling, rattling, or any other unsecured manner. This condition may result in excessive pressure during firing resulting in catastrophic breech failure.
A Battelle Pacific Northwest Laboratory study, released in August 1990, characterized particulate levels with both complete and partial penetration of the armor after hard impact. Researchers tested both the M829A1 and XM900E1 rounds and two non-DU rounds, the M865 and DM13. The purpose of the non-DU round firings was to evaluate DU resuspension during hard impact tests. The sample results were questioned when the percent aerosolized was initially estimated to be only 0.2 percent to 0.5 percent for the M829A1 and 0.02 percent to 0.04 percent for the XM900E1, values approximately two orders of magnitude below the expected values. One of the first studies Battelle performed with the XM774 produced a value of 70 percent, which is frequently cited in the popular press. This study stated it was highly unlikely more than 10 percent of the DU by weight aerosolized on impact. Duplicating other study results indicating a high percentage of the respirable dust from hard-impact testing was soluble in the lungs, this study indicated 57 to 76 percent of the respirable dust fraction was class "Y" material and 24 to 43 percent was class "D" material. (Class "D" materials have dissolution half-times of less than 10 days; class "W" materials have dissolution half-times of 10 to 100 days; and class "Y" materials have dissolution half-times greater than 100 days.) The resuspension tests indicated most of the resuspended dust was non-respirable, consistent with the theory the enclosure's filtering system removed most of the respirable dust.
A Battelle Pacific Northwest Laboratory study, released in July 1991, This study assessed the dose rate to which M1 and M60A3 crews would be exposed with deployed 105mm M900 cartridges. Researchers conducted the tests using worst-case stowage configurations and placed the bustle compartment near the driver. Rather than the mix of armor-piercing M900 and high-explosive (HE) cartridges, researchers filled all cartridge locations with M900 cartridges, an unlikely stowage situation. The researchers then calculated the crew members' dose to approximate the actual radiation fields with HE stowed appropriately and replacing the excess DU cartridges.
Based on this unusual configuration, dose rates peaked in the M1 at 0.5 mR/h under the turret bustle and above the driver's head and in the M60A3 at 1.5 mR/h in the vertical, exposed cartridge storage rack, as measured by portable radiation detection instrumentation. These levels are within the permissible levels of radiation in unrestricted areas. Using thermoluminescent dosimeters to measure specific points within the vehicle, researchers determined that the M1 commander, gunner, and loader received an average dose rate of about 0.01 mrad/h of penetrating radiation. The driver received an average dose of about 0.2 mrad/h with the bustle above him.
Dose rates to the M60A3 crew were slightly higher than the dose rates for the M1 crew. The commander and gunner received about 0.05 mrad/h of penetrating radiation. The loader, who had well-shielded cartridges behind him, but a stack of unshielded DU cartridges in front of him, received an average of about 0.2 mrad/h. The driver, who had cartridges on three sides, received an average of 0.28 mrad/h.
Assuming a crew occupied a fully loaded vehicle for 700-900 hours, none of the crew would be likely to exceed the 250 mrad/year administrative badging limit. Even with DU in all the 105mm ammunition slots, the only person approaching the limit would be the M60A3 driver, and this would only occur if the bustle were over his head during his entire time within the vehicle.
The study revealed that the drivers of both vehicles had the highest potential exposure. The M1 driver received his entire DU dose from the bustle of cartridges over head. (Note: Most of the time, the gun rather than the bustle is over his head). His dose, measured with the hatch open, maximized the radiation field. Without the bustle, the exposure to the M1 driver is negligible. On the other hand, the driver of the M60A3 gets only a small portion of his exposure from the bustle storage. Most of his exposure comes from storage in the hull. The study estimated that dose rates for more ordinary configurations are less than 0.05 mrad/h for the M1 driver and about 0.1 mrad/h for the M60A3 driver.
The Picatinny Arsenal, US Army Armament Research, Development and Engineering Center, Close Combat Armament Center developed an August 21, 1991 environmental assessment to address environmental concerns when the new XM900E1 APFSDS-T round, with its significantly greater armor-piercing capabilities, replaced the M833 APFSDS-T service round for the M68 cannon on the M60A3 and M1 tanks. The assessment summarized previous studies on radiological hazards, etc. conducted on the XM900E1. The assessment's conclusion was that only the testing modes for armor penetration and accuracy and final penetrator disposal presented any significant potential for environmental impact. The report also outlined measures to reduce the impact of testing. From a health and safety standpoint, the XM900E1 presents no greater risk than the existing M833. The XM900E1 program is not expected to have a significant environmental impact on air quality, water quality, ecology (flora and fauna), or health and safety to personnel associated with normal maintenance and life cycle operations.
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