I got to sit in on a symposium given by Wayne Van Zwoll quite a few years ago. It was a great little class small enough for Wayne to fully interact with anyone with a comment or question. He pretty much inspired the whole class to share personal hunting stories, methods and equipment. He's a great guy who's absolutely dedicated to anything regarding rifles, cartridges, reloading and hunting. Though not having anything to do with shotguns, I think these two titles by Wayne Van Zwoll you'll enjoy:
The Hunter's Guide To Accurate Shooting
and
Elk Rifles, Cartridges and Hunting Tactics
Another book I'd also suggest is an old one: "Mr. Rifleman," by Col. Townsend Whelen and Bradford Angier. It's an absolute classic, but sometimes hard to find.