User blog comment:Rozh/Surface-to-Orbit Artillery/@comment-131756-20110321005343/@comment-4791664-20110321043152

Do keep in mind Sir Isaac Newton: for every action, there is an equal and opposite reaction. Which is to say, given that massive force propels the slug forward, there is massive recoil. Also, there is no combustion involved: the slug is loaded and then propelled forward by electromagnets.