pull a gun
pull a gun on (one)
To draw a gun and threaten one with it. The mugger pulled a gun on me and told me to give him all my money. If you pull a gun on someone, you had better be prepared to use it.
pull a gun (on someone)and pull a knife (on someone)
to bring out a gun or knife suddenly so that it is ready for use against someone. I screamed when the mugger pulled a knife on me. The police shot the thief when he pulled a gun.