Hello experts I have quite a number of questions about a project that is basically an airgun, but uses the force of air/vaccuum instead of a spring to blow the air. Here is a brief description of the whole model: There are two tubes, one placed in the other, such that there is some space between them. There are two pistons too. The first piston operates between the space between the two tubes, and the other operates in the inner tube. Note that the inner ends of the pistons fit precisely in their vicinity such that air cannot move past either of them. These two pistons are connected together outside the tubes for convenience so that there is only one piston handle outside the tubes. The outer tube has an opening at one end (the end opposite to the piston handle) while the inner tube is tightly closed on one side such that when the piston is pulled back, vacuum is created in the inner tube. Now we have formed a machine which blows air with the force of vacuum. When the piston is pulled backwards, the space between the two tubes will be filled with air, while the inner tube will have vacuum in it. When the piston is released, the pressure of air will push the piston inside the inner tube (because there's vacuum in it). But since the two pistons are connected, the piston of the space between the tubes is also pushed forward, hence blowing air out of the opening. Now I put my questions: 1- Is this model practically attainable? 2- Which material should be used for the inside and outside tubes? 3- What are the advantages/disadvantages of this model against the conventional airguns which use the force of a spring to blow air outside a tube? 4- What should be the diameter of the inner and outer tubes if we want to blow a dart of mass 50g to a distance of 200m through this device? 5- Is there a company/firm where I can order this model? 6- And lastly, does anyone have an estimate of the cost of a prototype?