A method for controlling a servo for an actuator that applies a force to a piston that reciprocates in a cylinder of a free piston engine having axially-aligned cylinders and a pair of mutually connected pistons that reciprocate in the cylinders. The semiconductor element is surrounded by an at least partly electrically insulating housing. The housing has ends which mount to the existing lower receiver of the semi-automatic firearm to convert the semi-automatic firearm into a manual bolt-action firearm. A quote is extracted from the identified sentences and displayed to a customer in conjunction with information regarding the individual item.