I recommend V. M. Starr's classic little book, "The Muzzle Loading Shotgun, It's [sic] Care and Use". The book can be Googled. The book is a fascinating read from an old-timer who "had been there". About the only problem with reading the book is that spitting down loaded gun barrels and loading directly from flasks and pouches is no longer recommended. The rest of the information in the book is as timely as it ever was and it is presented in an enteraining and readable form.