Hammer Spring for Blackhawk

I know that this subject has been beat to death. And opinions vary. I understand "lock time", I think, and I understand heavy hammer fall. What I do not understand is the Ruger 23# main spring takes a "set" and accuracy falls off. Can someone explain that to me. I have tried 26# springs and my 69 year old thumb can't take it, 20# springs seem good. Any help is appreciated. Thanks, Jerry