4.1 grains does it for me. But I’ll say Sport pistol is just so-so in 38 special. ES is a little too high and other powders are more accurate. It is very clean. And I do use it in both 9mm and 38 short Colt for ICORE.
My favorite powder for 38 special is Ramshot Competition. I use it for NRA Action Pistol matches. Most accurate and least ES by far.