My neighbor has a 9mm Sigma that shoots dead-on for him. Of course he was an Army instructor for the 1911 back in the early 60's so he knows how to shoot. The problem is that at 69 he has some hand problems from injuries incurred throughout his life and now he has a problem racking the slide on the Smith. I thought I could put in a lighter recoil spring. The stock spring is about 18#. Whats the lightest that I could put in it. He doesn't do much target practice, just has it for home defense. When he does shoot it, he puts them in the center. Thanks for any help you can give me.