Big. Correct me if I'm wrong but basically what you are doing is putting the the go gauge. (Small one?) In with a piece of tape on it screwing the bbl down until it touches and tightening it to achieve minimum or nearly minimum head space? Then I'm assuming you check it with the no go to be sure you didnt make a mistake?
" Real elk guns start with the number 3 or bigger and blow two holes, one in and one out." - My Dad