You can’t create a machine gun yourself, or even buy one on the open market.   Do you mean a gun like that?  Would you like to learn about it, and what it’s for?
assistant
That sounds like you want to make a weapon that fires rapidly, such as a machine gun.  Do you mean like this: http://i.imgur.com/ItwBe2b.jpg ?
assistant
How can I create my own machine gun?
user
I'm sorry, I don't understand your question. What do you mean by a machine gun?
assistant
A gun that fires rapidly.  I want to make one for myself.
user