"Firearm Anatomy Book III: The Remington Double Derringer" by David S. Findlay
Available through Amazon:
https://amzn.to/4daGdYy

David S. Findlay is a firearms designer with extensive experience - a decades-long career in the field working for Remington, Marlin, S&W, and Kimber and two dozen patents to his name. In this, the third book of his "Firearms Anatomy" series, he takes on the Remington Double Derringer. Not quite as sexy or exciting as the submachine guns that were the subjects of the first two volumes, but this is only superficially about the derringer. In fact, this book is an essay of guidance and advice to aspiring designers.

Sure, the bulk of the book does indeed use the Remington derringer as its subject matter. It examines the design flaws of that classic piece, the choices that led to those flaws, and the potential safety mechanisms that could have been included - and would have to be if it were introduced commercially today. It also gives a nice analysis of the .41 Rimfire cartridge the derringer used, looking at both original ammunition and the Navy Arms later production. And for anyone who really has the hankering to make one, 97 pages of technical drawings for it are included in the book (they are nearly half the page count).

But really, nobody is actually looking to re-engineer the frame hinge of a gun that ceased production in 1935. This and other examinations are case studies to show the process of arms design and testing because they apply just as much today as they did when Remington introduced their derringer in 1867.

So if that sounds like the sort of mentoring you are looking for, then you will definitely want to pick up the book. It's a short read, but full of valuable advice and insight. It's available on Amazon for $34.95 at the time of this writing.