Abstract: A series of normal and oblique penetration experiments were performed to explore the dynamic response of slender projectiles penetrating into typically hard targets. In the experiments, the parameters of the ogive-nose steel projectiles are as follows: the diameter is 14 mm; the lengths are 168, 112 mm; the dimensionless wall thicknesses of the cartridges are 0.1, 0.15; the head factors are 3.0, 4.5. The projectiles were made from 30CrMnSiNi2A and were launched by a light gas gun with 57 mm diameter impact velocities of 100~250 m/s. The processes of impact and projectile deformation were photographed at up to 2104 s-1 using a photron fastcam. The recorded information indicates the following five different structural failure modes for a slender hollow projectile penetrating a typically hard target: (1) local bulges near the dangerous sections on normal impact; (2) plastic buckling on the especial sections without local bulges on normal impact; (3) plastic bending along the deformed region on oblique impact; (4) local plastic bulges coupled and local plastic buckling coupled with generally plastic bending on oblique impact. The penetration modes were established based on the cavity expansion theory. And the control equations were given, which can be used to calculate the yield function in a rigid-perfect plastic free-free beam section subjected to dynamic lateral loading and axial loading. The calculated results are in good agreement with the experiment.