If this is any help I copied this off the Wolff web catalog:

Recoil Springs

For Use in:
645, 745, 4506, 4526, 4546, .45ACP

Reduced Power : 8, 9, 10, 11 & 12 Lb. (Variable)
Factory Standard : 14 Lb.
Extra Power : 15, 16, 17, 18, 20, 22 & 24 Lb.

Recoil Calibration Pak below includes 1 each of 15, 16, 17, 18 and 20 pound extra power recoil springs. 3 extra power firing pin springs are also included.