[SOLVED]Measure FPS Without Chronograph

Hi!
I've run into a slight problem as I don't have a chronograph to measure the FPS of my .25 FX Wildcat.
It's tested and specified to be around 910/Fps with the pellets that I've got. Should I take their word for it or do I have to find a way to measure?
Sadly there is no community for air rifles in my area(not even close) so I can't borrow.
Has anyone got any idea how I can measure without a chronograph?

-Krister

EDIT: Typos