I fit 'tight', as in flush, since trying to get .001 often turns into 'more'. The barrel and action also works/seats in so working to min. clearances is my preference. I use a randomly picked 10 cases for fit and measure the rims to find the way they tend to run. After all is up and running if I hit a thick rimed case, it gets touched with a fine file on the inside of the rim, or just set aside.