The author of this book prides himself of not having a formal education and it shows. You will find no useful technical information necessary to safely design, build, and test firearms.
What I didn't like about this book: Outdated information about firearms laws, hand drawn technical drawings (get a DELL dude), no information on new manufacturing technologies such as composite materials or CNC, total lack of technical information, single page on marketing of firearms. (There is more but I stop here)
What I did like about this book: It has a shiny cover.
If you are looking for real information on the engineering of firearms look elsewhere.