I bought a metal cutting hole punch on Amazon for use on brass. Turns out it also does well on plastic, leather, gasket material, etc. Punches sizes up to about 3/8" neat as you can want. Think it was about $30. Makes the work go pretty quickly, also because there is a small pin set in the dead center of each punch piece. You just put that in the center of what you're punching and there you go.
