Concrete, sandstone, and, in a previous round of experiments, pumice, were tested under hypervelocity impact at SwRI. Aluminum spheres with diameters of 1 and 1.75 in were shot at a velocity of approximately 2 km/s using a 50-mm conventional powder gun. The targets were mounted on a swing so that the momentum enhancement could be measured. The size effect, i.e. comparing momentum enhancement generated by the small and large projectiles, was of particular interest in this project. The targets were also scaled, although for sandstone we were limited by the natural geometry of the rocks. The results from the experiments show a clear size effect for the concrete while sandstone did not show any size effect, possibly because of experimental artifacts. The sandstone behavior was investigated with computations using the EPIC hydrocode. The porosity and compressive strength of the sandstone used in the impact tests were measured and reported. The rock is very similar to one reported and extensively tested by Lawrence Livermore Laboratory in 1974. Two material models (Holmquist-Johnson Concrete and Johnson-Holmquist-Beissel) were fit to the data from LLL. The momentum enhancement predicted by the code is reported for different parameter studies.