What are the minimum and maximum pumps and why does it matter?

Most multi-pumps specify a minimum (usually 3 pumps) and a maximum (often 8 to 10).

Below the minimum, the seals do not seat and pressure can leak past or cycle improperly. Above the maximum, you stress the seals and reservoir and can lock the valve so it cannot open. Going past the manufacturer's max gains you almost no extra velocity (often only 5 to 15 fps for the last pump on most guns) at significant cost in wear. Stick to the published range.