The contact breaker points on our old magnetos are mechanical switches, usually opened by a fibre heel running on a cam and closed by a return spring. That’s the simple explanation but the design of the system is actually a compromise.
From a mechanical wear point of view, the points would ideally open and close gradually and could be achieved by making the opening and closing ramps of the cam a gentle smooth transition. However, from an electrical point of view, the points need to open very rapidly in order to ensure that, by the time the condenser has done it's job, the points would be open enough to ensure that the low tension current could not jump the points gap.
When the points are closed, the fibre heel is clear of the cam so when it hits the rising edge of the cam, it is not unusual to find that the moving point bounces, the fibre heel jumps clear of the cam and the points open to considerably more than the set points gap.