I agree with Ross, you will want to try a variety of springs to see what lets you regain your sight picture fastest. This will be a very subjective experiment, no two people seem to prefer a specific weight and you will be limited somewhat by the mechanical needs of your weapon. When someone comes to me to tweak out there gun I have a tackle box with *a lot* of springs in it. We go to the range with a bunch of ammo and put one spring in, fire a few strings, try another spring, fire a few strings...etc. until we find what he or she likes. So then they know that a Wolff 13 pounder is what they want for that gun with that load, thats what they stock up on.

-Mike