I use whole pork butts . A whole pork butt is around 80 / 20 . So 80 % lean and 20 % fat . That's enough to do sausage , so I don't add any extra fat .So where do you get the extra pork fat? Don't you want 30-35% fat content?
The 30 % you ask about is a not to exceed number , upper limit of the fat content range .
So if you do try it , buy a pork butt . Grind the whole thing and mix it into itself , before dividing it into batch size , because the butt as a whole is 80 / 20 .
This is one butt ground . Plenty of fat in there .
Mixed and stuffed . You can see the fat definition .