M774 105mm, APFSDS-T
The 105mm M774 is a high velocity, long 1/d, fin stabilized projectile. In the mid-1970s, it became evident that the latest generation armor was impervious to tungsten carbide penetrators. Picatinny engineers had been working on improving the properties of DU, an especially dense metal, and saw potential for its use in the 105mm M774 cartridge. In conjunction with the Department of Energy's Battelle Pacific Northwest Laboratories, Picatinny developed the unique material purity and heat treatment process necessary to produce a hard, touch U3/4Ti, Uranium/Titanium alloy penetrator.
The 105mm kinetic energy rounds consist of three models, M774, M833, and M900. These are armor-piercing antitank ammunition and are intended for use in the 105mm, M68 gun and are loaded and fired in the normal manner. The projectile is fin stabilized in flight. 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 subprojectile consists of a monolithic staballoy (depleted uranium) core which is fitted with a steel tipped aluminum windscreen and an aluminum fin assembly.
In the early 1980s test firings by LCWSL at Yuma Proving Ground, Arizona, revealed that the stabilizing fins were being severely reduced in span due to aerodynamic heating. In 1983 a computational study examined the in-depth temperature response of a thin, swept fin to aerodynamic heating for a series of fin geometries in an effort to determine if a minor design modification can be found which will result in improved performance of the swept fin. The computational results indicated that the aerodynamic heating can be significantly reduced by a relatively small increase in the sweep angle of the fin.
Fin stabilized kinetic energy penetrator projectiles, such as the M774, have occasionally suffered from severe reduction in fin span due to inbore heating, inflight aerodynamic heating, or a combination of both. This report describes a computational investigation of the inbore and inflight thermal response of the M774 modified swept fins of aluminum and steel composition. The calculations demonstrate that both the inbore and inflight heating of the fin are significant, and that the steel fin shows an improved thermal response over the aluminum fin.
A 1989 study [Wilsey, Edward F. and E.W. Bloore. M774 Cartridges Impacting Armor-Bustle Targets: Depleted Uranium Airborne and Fallout Material, BRL-MR-3760. Aberdeen Proving Ground, MD: Ballistic Research Laboratory, May 1989.] was one of several conducted on the M774 ammunition (105mm). It addressed only one objective-the documentation of the amount of DU aerosol and fallout around and downwind of the armor-bustle target. "Very little of the depleted uranium of the M774 penetrator left the immediate target area as an aerosol." The highest value-regardless of the wind conditions-was so low that over 1,400 such tests would have to be fired in a week before tolerance limits would begin to be reached. While the threshold limit value was exceeded when the cloud passed over the samplers, the time-weighted-average exposure for a 40-hour workweek was only 0.07% of the occupational Threshold Limit Value.
Battelle first released the report Gilchrist, R.L., P. W. Nickola, J. A. Glissmeyer, and J. Mishima, Characterization of Airborne Depleted Uranium from April 1978 Test Firings of the 105mm, APFSDS-T, M735E1 Cartridge, PNL-2881, Richland, WA: Battelle Pacific Northwest Laboratory, 1979 (initial release), June 1999 (publication date) to the US Army in 1979 but the project office decided not to publish it then. Due to the interest in the historical Depleted Uranium testing program and the uncertainty associated with the frequently-cited 70 percent aerosolization figure, in June 1999 Battelle decided to publish this report.
This report is a follow-up to the hard target impact testing of the M774 and takes advantage of the field experience and difficulties faced in that 1977 test to improve test conditions and sample collection. This second test, conducted in 1978 at Ford's Farm within Maryland's Aberdeen Proving Ground, was more successful in characterizing the impact cloud plumes, as well as measuring time-integrated concentrations (TIC) with time since impact and particle size distributions. Uncertainties so prominent in the M774 report are considerably reduced in this M735E1 evaluation. In this test, the 105-mm M735E1 cartridges were fired at a series of three armor plate targets located about 200 meters away. The impact and penetration of the projectiles caused a shower of fragments and considerable airborne particulates. This projectile assembly contained a 2.2-kg DU core. The aerosolized fraction of the M735E1 penetrator from target impact ranged from 17 percent to 28 percent.
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