What do you mean by break in?
I fired mine about 15 times sighting it in at 100 yards. It shot really well with 3 Triple Seven Pellets and 250 gr Shockwave Sabots. I'm not messing with mine anymore.
If you are going to fire patched round balls or something else, I can't help you there.
I just cleaned mine real well before I went to the range the first, made sure the bore was dry, fired a couple primers to make sure the bore ignition hole was clear and dry.
JW