KP97DC, With the modern metals now used in hand guns, there really isn't such a thing as break-in anymore. With the older guns where softer steel was used, a shoot 10 & clean, shoot 10 & clean, etc for 50 rounds was the norm. Some folks still like to do a break-in regimen. It doesn't hurt a thing but it doesn't seem to help either. Your P-90 barrel will be "broke in" after 50 rounds and should last for 10s of thousands of rounds.
Modern rifles are pretty much the same, however, bench rest shooters still do the break-in routine. Most will shoot 2 rounds and clean, 3 rounds and clean, shoot 5 rounds and clean, then 10 rounds and clean. After a box of 20, the bore is broke in. I seriously doubt there is any difference in bore condition or life expectancy if you were to shoot all 20 rounds before cleaning. What ever method you use, make sure the cycle rate is not more than 1 round per 10 minutes.
The secret to barrel longevity is to clean the bore after each shooting session no matter what kind of gun you are shooting.