High FPS can be achieved when:
- enough air is being sucked into the cylinder.
- the cylinder is large enough to accommodate the required amount of air.
- the spring can move forward fast and powerful enough to create the necessary air pressure.
- the compressed air does not escape.
- the hopup unit does not introduce too much friction on the bullets.
Frankly, there is no single best way to measure FPS. It is believed by many that the more accurate way to measure FPS is through the use of a chronograph. The problem with this method is that rarely will the chronographed speed correlate to the actual bullet velocities of your setup. Without proper calibration, no two chronographs will clock the same velocity.
The soda can test is not for measuring muzzle velocity in an accurate manner. It may produce inconsistent results under the use of different BBs and different hopup settings.