I have a number of 9mm handguns and I have slugged the barrels on all of them. From that, I size .356". I have run limited Ransom Rest tests with identical loads and found increasing the bullet size and the group size increases also. I know some say they shoot bullets several thousands over sized and get better accuracy, but I would like to see that put to a test. This is what I like about the Ransom Rest, it takes out the human element.
I probably could size .355" since my barrels are likely close enough, but since I built and use a pneumatic sizer for speed and less effort I use a Lee push through sizer, not readily available in .355'. I have several 9mm loads that will deliver 1-1/2" and under groups at 25 yards with my .356" bullets, so I don't plan on spending the time, effort or money to find out.