[pfreivald]

We tried two 40-lb constant force springs from McMaster-Carr on a prototype shooter, and the exact same design (including the same pull) with surgical tubing threw the ball much, much farther.... I think there's a speed-of-wind-up and the sheer inertia of the things to take into consideration, there.

Also, trying to interweave them proved downright dangerous last year, so we had them on the same shaft, but side-by-side. Be very careful with these things!