For a .45 acp, SD or Duty pistol, I use 19 or 20lb, that extra punch works to give hollow points that little extra, to jump the ledge into the throat of the chamber, But the resistance of the slide on recocking the hammer, is part of the equation as well, as the slide moves rear ward, it must recock the hammer, against the hammer spring, ( I don't recommend lightening the mainspring ) unless your going full game, and will not use that pistol for SD or Duty. But you can make this operation, less resistant, rounding the firing pin retainer and slide on the bottom helps, plus polishing the hammer face where the slide and hammer come together, and watch for the slide overcocking the hammer, too much movement, beats the hammer hooks to death, sometimes removal of metal from the hammer face at just the right spot, makes the resistance much lighter, and you can feel it when operating the slide.