Once one correctly cleans and then relubes the gun, the only real "break in" is running a couple hundred rounds through it to verify it functioning correctly. The couple hundred rounds is to allow the various parts to wear against each other and smooth out any rough spots which may affect proper functioning. Once that is complete, I do the same thing with several boxes of the carry ammo I plan on using as that can have a different bullet profile and cause feeding problems. By the time I have several hundred rounds through the gun I pretty much know if it is going to be dependable or a dog. The 4 XDs I've owned have all performed superbly but one can always find a dog in every bunch and it pays to do the testing.