Are you wanting the process of regulating a double rifle, or are you asking about the working up a load to shoot to the regulation of a double rifle? They are two intirely different things,though most have a bad habit of useing the word regulateing for both.

I suspect you are asking about the physical act of regulation of a barrel set, with wedges, and and solder! The Alexander Gray Book "The Hammerless Double Rifle" is a good start, but will tell you only the H&H method, which is my way as well, but there are others that work as well! If you are asking about working up a load to shoot to the regulation of a double rifle, then Graeme Wright's book "Shooting The British Double Rifle" is the book to buy! Both, however are MUST READs for anyone interested in double rifles