I recently bought a Bialetti 4 cup stainless moka pot and a Baratza Virtuoso and my first attempt at making my own grounds came out badly. I have some Illy to compare so I got my grinder to produce grounds that felt and looked similar in size. The grounds did clump a little bit when I got it to what looked like a similar grind size compared to the Illy grounds.
I put the grounds in the basket, about 3-4 table spoons and leveled it off with my finger. I the pot on the stove and the resulting product was thin, unlike what I got with the Illy grounds, and horribly bitter. The body was closer to what I get out of my Melitta style pour over than espresso.
When I went to clean my pot, I noticed that the grounds in the basket only filled about 2/3 of the basket which was completely unexpected. Normally I get a tightly packed puck all the way to the top of the basket when I use the Illy coffee grounds.