A basic understanding of headspace and how it affects the proper operation of a firearm are necessary if you wish to call yourself a gunsmith. Otherwise all you will be able to do is change parts with the hope that somehow the problem will go away. The later is normally called an armorer, not a gunsmith. Many self proclaimed experts try to create fear and confusion around the subject of headspace. This subject, like most measuring processes, is simple and easy to understand if you are willing to educate yourself.
In a broad sense, headspace is a complex relationship between the cartridge, chamber, and firearm mechanism. The starting point for headspace is the cartridge case. The complex functions of the cartridge case include holding the cartridge components together, aligning the bullet in the bore, expanding to seal the breach from gasses, contracting in time for easy extraction, and removing heat from the chamber. Then of course we have to discuss the chamber and all its attributes. This booklet contains all the information a gunsmith needs in order to understand headspace and diagnose issuse that may arrise with ammunition and chambers.