A way to measure force...

[KenWittlief]

its not really force you are looking at - a bathroom scale measures force (the force that gravity is exherting on the mass you are weighing)

you need to measure the impulse that results from a collision - the energy contained in the projectile

another way would be to fire the projectile straight up, or to use a strobe flash on a camera and measure the velocity as the projectile passes.

or setup a light sensor light gate, with the projectile passing infront of two light sensors, spaced out a few feet apart

[Billfred]

Originally Posted by KenWittlief

or setup a light sensor light gate, with the projectile passing infront of two light sensors, spaced out a few feet apart

Wouldn't one photogate work, if the object to be measured has a known length? (That's how I think I recall us doing it in high school physics, combined with a 3-by-5 card.)