YouTube - ‪STI40.MOV‬‏
As other have said, find the bullet weight and brand of ammo that shoots best for you. It may not be the same ammo for each gun. My S&W 310 likes Mag Tech 180 grain better than any other .40 ammo that I have tried in it. The .40 auto in my YouTube video (ABOVE LINK) shoots .40 Remington or .40 Winchester to point of aim (POI) at 25 yards. It shoots the Mag Tech 1" to the left of my POI.
Mark