The method and experimental results of investigations of shaped charge liner reduction during early stage of collapse are presented in this paper. The liners made of sintered copper with porosity of 6, 8, 10 and 15% were examined. The tests for two variants of loading pressure were carried out. From the research it follows that during early phase of liners collapse, the decay of pores does not occur. Verification of experimental results, on the basis of theoretical model of compression of porous material, was made.