I need to build a projectile launcher which can launch a marble , mention angle , how to build?

Here is how to get the best device...Use what ever your going to for your propellant ..I have used propane,compressed air, ether and black powder..every one has its drawbacks..The biggest drawback is the fact that the marble fits the barrel in a terrible way. So I have found that if i use a SABOT pronounced Sayboe ,,you can set the marble into the end of a 12 ga shotgun plastic cup wad and then breech load with a ramming rod. The best angle is just above 45 deg..about 49-50deg..since the projectile is still rising for a short period (fly time) is increased...if the marbles are able to be inspected get some that are consistent gl not clay or stone... If black powder is th propellant use a cap made for the purpose. if propane or ether is used ignition can be accomplished with a barbeque capacitor spark lighter...either way the Sabot and barrel need to come from a 12ga shotgun..300-500yards is not uncommon...Let me close this by saying ..this is the the most dangerous thing a non-professional person can be fooling with ether in a closed room or propane or black powder will KILL YOU..If you not fully Competent or have someone who is please just feel good that you know that it can be done and leave it at that...A marble is a simple tool in a kids game , shot from a cannon its a deadly weapon..ASk David or better than that Ask Goliath...From the E