There are probably 2 answers you'll get:
1) load it and fire it a LOT!!!
2) Go the fire 1, clean, fire 1 clean, fire 1 clean..............yadda yadda yadda method.
I would suggest a compromise: Clean the barrel well before shooting. Then fire 5 shots, clean with something like Butch's Bore Shine (which will get after copper somewhat), fire 5 and clean again. Then Fire 10 & clean. Fire 10 more and check the bore - if it's really no more fouled than after the previous 10...................then it's ready for normal range work. If it's dirtier or as bad, Try another 10/clean pattern.