C-shaped armatures are widely used in railguns. The transition speed of armature determines the performance of railgun, which makes increasing transition speed the main goal in armature geometry design. The trailing arm's length is considered as one of the most critical parameters in armature geometry. In this paper, experiments using monolithic C-armature of the same material (Al-6063), which had trailing arms of different lengths - 15, 20, 25, 30, and 35 mm, were performed in a 20-mm caliber railgun. The maximum amplitude of driving currents under which these armatures launched without arcing was measured in launching experiments. Moreover, the length and positions of actual contact surfaces on armature trailing tails were compared by in-bore experiments. Results indicate that the increase of trailing arm length (from 15 to 25 mm) results in a significant increase of nonarc driving current; when the length exceeds 25 mm, this increase stops, which may be caused by the geometry deformation of armature in launch process. Two improved geometries of trailing arm, which were tested having good performance in rail launch experiments, are presented.
