Easy pendulum lab question?

In theory, the m of the pendulum has no effect on the period. The length of the rod (the string from the pivot point to the bob), the force of acceleration of gravity, and the angle of the swing (amplitude) all affect the period. In reality, the more m of similar materials will create more drag and will affect the period of the swing. Increasing the m by using a denser material should prevent this from happening, or doing the experiment in a vacuum would also work to eliminate air friction.