There the how and why of working better.
2fg courser granulation makes for a slower build up of gas pressure which the long barrel of a rifle can take advantage of to get more velocity.
2fg fired in the short barrel of a revolver shows a lot more still burning (gas making) powder being ejected uselessly into the atmosphere.
3fg makes the revolver MV a little higher as more powder gets burned in the short barrel.
No matter the powder granulation size, the total gas volume produced will be the same for the same mass weight (not volume) of powder. There is just a faster gas creation (release) with the finer powder granulation.
The quicker burn time will spike chamber pressure higher with the finer powder granulation which makes more MV in the short barrel pistol.