A flash in the pan: the part of a flintlock musket that held the firing powder was its pan. Sometimes the primer flashed but did not explode, so the action did not result in a bullet being shot. Various political candidates have proven themselves to be a flash in the pan because they look brilliant for a brief moment but never accomplish anything.
A real pistol: pistols are quick to load and shoot. If you are a real pistol, you are fun loving and high spirited. Granny Clampett from the Beverly Hillbillies was a real pistol.