The 30 ○ oblique impact between a high speed copper rod and a moving steel plate is investigated. The numerical simulations are carried out in the second order, multi-material Euler-Godunov processor of Autodyn V4. The full three dimensional calculation is compared to an approximate, two dimensional plane strain simulations. The results are compared to available experimental data. The three dimensional effects are considered and the validity of using the 2D approximation is discussed.