A controlled aperture ball drop includes a ball cartridge that is mounted to a frac head or a high pressure fluid conduit. The ball cartridge houses a ball rail having a bottom end that forms an aperture with an inner periphery of the ball cartridge through which frac balls of a frac ball stack supported by the ball rail are sequentially dropped from the frac ball stack as a size of the aperture is increased by an aperture controller operatively connected to the ball rail.