Smylee is spot-on with the crown and loading tighter combinations without cutting the patch.
This how-to with the resulting picture of my 20 bore's muzzle should help with the crown.
Rotate the barrel every 10 to 15 wrist 'twists' of the emery. I also use 320 wet/dry- whatever is handy at the time.
A couple patches just below the muzzle, will catch the sand-paper or emery's 'dust', which comes out with a worm,
or dental pic. Those are most useful in a shop - I get them from my Dentist's hygienist, who saves them for me.