An electrical energy-insulating, preferably ceramic, insert (15) which is fitted in a barrel (2) is adapted in order to prevent electrical energy transmission (16) from an electric igniter (3) to a barrel body on firing of an ammunition unit (11) which can be initiated with the electric igniter (3). The insert is arranged in a position for firing of the ammunition unit. By means of the invention, a simple solution is obtained to the problem of electrical energy transmission by virtue of the fact that other measures do not have to be taken, for example the cases of the ammunition units do not have to be adapted by complicated and cost-increasing measures.