For the C-type armature rail gun, in order to ensure good metal-to-metal contact between the armature and the rail, it is necessary to optimism the design of the armature structural dimensions and the pivot-rail interference. In order to study the influence of the structural dimensions of each part of the armature on the contact characteristics and current distribution, a finite element model of the rail gun considering the initial interference contact of the armature and rail is established to calculate the contact characteristics of the armature and rail before launching and the distribution of the current density during launching; the structural dimensions of the armature are changed to study the influence of the changes in the dimensions of each part of the armature on the contact characteristics and current distribution. The results show that the pressure distribution on the contact surface of the armature-rail is not uniform, the current distribution characteristics of the contact interface are similar to those of the contact pressure distribution, and the current density distribution is concentrated at the rounded corners of the armature throat; the change of the size of the armature structure has a greater impact on the contact of the armature-rail interface, and the change of the radius of curvature of the throat can make the current density distribution more reasonable.