A power charge for actuating a wellbore tool. Combustion of the power charge generates gas and corresponding gas pressure within the wellbore tool and the power charge and wellbore tool are configured for providing a path to an expansion chamber for the gas pressure. A body of the power charge may have the shape of a regular polygonal cylinder, thus defining flow-paths for the expanding gas. The power charge may include a cylinder of energetic material and an interior space formed within the energetic material and configured for receiving an igniter and/or ignition material. Ignition of the igniter or ignition material results in combustion of the power charge.