Recommendation 7: The spatial variation of modeling clay is significant and three-dimensional. The response of the clay appears to depend on temperature, shear history, and proximity to the edge. Given the confounding effect of box geometry, the Aberdeen Test Center should perform a systematic set of column-drop performance tests as experiments to assess the consequence of variation due to the shape and size of the frame that defines the clay box. These tests should determine if a circular box of approximately the same area as the current box reduces the spatial variation that affects ballistic testing, or if a larger box area eliminates the clay edge effects that affect ballistic testing.

Recommendation 8: As an alternative to the current column-drop performance test the Army should quickly develop and experiment with a gas gun calibrator, or equivalent device, that delivers impactors to the surface of clay boxes and that determines local variation within a clay box at speeds and depths corresponding to those involved in the generation of the backface deformation. These experiments should be used to estimate as accurately as possible the variation of backface deformation measurements both within a given box and between boxes, under realistic testing conditions using existing test protocols.

Recommendation 9: While the committee applauds the Aberdeen Test Center efforts to understand and attempt to measure the dynamics associated with the creation of a backface deformation, the signal-to-noise ratio of the flash x-ray cineradiography approach should be thoroughly analyzed to determine if the desired spatial and temporal resolution can be achieved.

Recommendation 10: To better understand and measure the forces that create the backface deformation the Army should experiment with inserting microscopic temperature and displacement sensors into the clay near the site of the backface deformation.

Recommendation 11: The Army should consider experimenting with high-speed photographic analysis of backface deformation in ballistic gelatin as an alternative for providing needed information on the forces that shape the backface deformation.

Recommendation 12: The Army should conduct rheology and other studies on ballistic gelatin as a mid-term alternative to modeling clay due to its properties, which include the ability to directly record BFD using high-speed photography and the elimination of the effects of shear history, time, and temperature on the response of the backing material. However, correlation studies and tests are needed to better understand the differences in the extent of deformation and dynamics among gelatin and alternative clay formulations.

Recommendation 13: The Army should perform rheology and other evaluations on microcrystalline wax mixtures as a possible long-term replacement for Roma Plastilina #1 as a backing material for ballistic testing. Studies are needed to



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