To pursue VNIIEF–VNIITF joint investigations, this paper briefly describes the experimental setup and provides numerical 3D-computation results (LEGAK-3D technique) on special features in the convergence dynamics of steel shells under their quasi-spherical explosive loading in the system with the 40-mm outer radius of the explosive layer. The computation results were compared with the data experimentally registered for shells of the 30KhGSA steel, both as-received and quenched to HRC 35…40, and the austenitic 12Kh18N10T stainless steel. The comparison was also made with laser-interferometry results obtained directly under explosive loading, as well as with gamma-tomography and scanning electron microscopy investigations of the recovered shells.