A way to measure force...

[Dick Linn]

Check this: http://www.gigapxl.org/

Go to the image gallery, pick any picture, then scroll down and look at succedingly zoomed views and look at the detail. In this case, I don't think they are enhanced in any way. It's equivalent to a 4 Gigapixel camera! Now think of what detail image enhancement could show.

Back on topic, just shoot the balls into a pendulum of known dimensions & mass and calculate from there. Now think about what the mass of the pendulum should be relative to the projectile to achieve maximum transfer of momentum and avoid losses.