Thin-walled square columns are generally used as impact energy absorber in automotive structures due to their ease of fabrication and installation, high energy absorption capacity in terms of progressive plastic deformation and long stroke. However, the main drawback of standard square column is the high initial peak force. An external tapered plunger is proposed to overcome this shortcoming while at the same time, improving the impact performance. Static and dynamic axial crushing were performed by theoretical and finite element analysis to determine the initial peak force (IPF), crush force efficiency (CFE) and plastic specific energy absorption (SEA) of columns with external plunger of various taper angles. The simulations results were validated by experiments. It was found that the external plunger significantly enhanced the column impact performance and the deformation characteristics as well. Comparison with plain square column was carried out and it was found that the concentric plunger reduced the initial peak force and increased the crush force efficiency for both static and dynamic loading conditions.