Greetings to all Forumites !!! I am new to this forum and this is my first post. If the subject of my post does not concur with this section, pls excuse me and redirect me to the correct section. Thanks. My interest is in ballistics, particularly internal. Most of my questions and discussions will relate to airguns, although I'll discuss the physics here and not mechanical setups. I hope this subject is not taboo. I should like to start off with this question : Using ONLY compressed air from a reservior, is it possible to let out a stream of air through an orifice faster than the local speed of sound ? I know that a CD nozzle can do it, any other way ?