An electron beam (EB) gun assembly for an EB furnace is provided. The EB gun assembly includes an EB gun-frame assembly including a skeleton frame and at least one EB gun mounted to the skeleton frame, and the EB gun-frame assembly is configured to rigidly mount onto a first EB chamber lid and melt material in a first EB chamber and be removed and rigidly mount onto a second EB chamber lid and melt material in a second EB chamber. In some forms, the EB gun assembly includes at least one mounting frame and the at least one EB gun is mounted to the at least one mounting frame and the at least one mounting frame is mounted to the skeleton frame.