A powder-driven connecting tool for connecting power lines is disclosed, as are assemblies and replacement parts for such a tool. The tool includes a tool head with an anvil, and a power unit with a ram. A breech cap assembly connects to the power unit and includes a sleeve threaded on both ends and a cap threadedly mounted on one end of the sleeve. The sleeve and cap define a breech for a powder charge. An adapter is mounted on an outer end surface of the cap. The adapter is narrower than the cap itself and is adapted to be driven by a power tool in order to tighten and loosen the cap and the sleeve. The adapter may, for example, have the form of a hex nut.