I've come across this question a lot on forums and in books and magazines. The general consensus from what I've read suggests that a person put 200 rounds of the ammo they plan on carrying through their gun. This is to test reliability and accuracy. This can be quite expensive, but you may end up betting your life on your gun/ammo combination.
Manufacturers recommend a certain number of rounds for break in on some pistols. I have a Kahr CW9 and they recommend 200 rounds of regular ammo to break in the gun before you consider carrying it concealed.