Abstract: A gas operated semi-automatic rifle is disclosed having a forwardly moving gas piston located under the discharge end of a barrel. The gas piston is connected to a locking mechanism. The locking mechanism is engaged with a breechblock. As the gas piston moves a short distance forward after a round has been fired from the rifle, the locking mechanism moves rearward and disengages from the breechblock. The breechblock is biased rearward by being disengaged from the locking mechanism. The breechblock strips a new cartridge from a magazine, and reloads the rifle.