I tried grinding some supermarket Starbucks beans (just to experiment, you understand!) on the one but finest setting on my new Dualit burr grinder, and the grind looked very fine, and worked very well in the Aeropress - very little drip through to begin with, but not hard to press, and everything seemed OK.
I then tried roasting some beans (my first attempt!) in a Prima popcorn popper - some Brazil Camocim Iapar from HasBean - did a medium roast, as suggested, left to de-gas, ground on exactly the same setting (one up from finest), but in the Aeropress I found it practically impossible to press, like the grind was way too fine, and I also ended up with about half the amount of liquid in the cup compared to the 'cheap bean' grind, as though the coffee grounds had retained a lot more of the water. The coffee still tasted great (lovely nutty flavour) but was perhaps a little weak, probably due to the difficulty pressing it and 'losing' some of the water in the coffee grounds.
So why would this happen when I ground on exactly the same setting on both? I'm new to this, so maybe I'm missing some basic coffee princple! Could it be caused by under/over roasting?