Today we had a customer pick up a newly purchased semi-automatic handgun. Her pistol was an excellent choice for her -- a quality gun from a first-tier manufacturer that fit her perfectly. We were talking about ammunition selection and she asked a very pertinent question -- "Why do I need to break my gun in?" This led to an excellent discussion on the need to use your defensive handgun on the range in order for the shooter to become familiar with it as well as to ensure that the firearm is reliable with the selected defensive ammunition. Generally from 200 - 500 rounds are viewed as necessary to break-in such a defensive handgun. A very few initial failures may be considered acceptable as the gun is brand new and tight. But the last 200+ rounds should function flawlessly to give the user confidence in a practically 100% reliability rate. Breaking-n should be done with good quality factory-new ammunition. Of course it goes without saying that the gun should be cleaned and well-lubricated. Initial break-in may be done with target-grade ammunition but the final ~200 rounds or so should be done with your self-defensive ammunition -- which is obviously much more expensive. But this investment is considered to be essential for a safety-critical defensive pistol.
See the link below the photograph for a more comprehensive article on this important topic: