Operation and Use of the Defensive Shotgun, John Farnam, 1990, Defensive Training Productions, 715-235-6503
Farnam observes that the shotgun is far more powerful than any handgun. Not only is it more powerful in terms of firepower, it is also more powerful in terms of the power of persuasion (including the persuasive sound of a pump shotgun being racked).
Ammunition
While shotguns can be chambered with a wide variety of ammunition, Farnam says that 12 gauge is the most common choice among police. He explains what 'gauge' means and then talks a bit about different pellet sizes. He recommends 00 buckshot as the most effective choice at ranges up to 25 meters. He also talks a bit about birdshot (fine for birds and rats), CS gas, slugs, rubber slugs, and other gauges. His recommendation for 12 gauge 00 buckshot is Remington 2.75 inch, 9 pellet. He also dissects a 12 gauge cartridge, explaining the purpose of each part.
He then covers the various topics summarized below.
Accessories: plastic stock and fore ends (yes), pistol grips (yes), rifle sights (tend to snag, usually not needed), bead sights (usually just fine) and slings (sometimes indispensable, often a nuisance).
Spare Ammunition: bandoliers (preferred), shell-holding stocks (all right), side-saddle types of shell caddies (just get in the way).
Pumps Versus Semi-Autos: pumps often the best choice as they are easy to transport it in a safe state (magazine charged, chamber empty, hammer down), yet it can be made ready very quickly. Considers the Benelli Super 90 an excellent auto-loader.
Carrying the Weapon: port arms, low profile, high profile
Fire positions: point shoulder and assault form
Arming the weapon (as you assume a firing position please)
The four conditions of a shotgun (clear, loader safe, armed, armed safe).
How to charge the magazine, how to load the gun (chamber a round), going from 'armed and ready' to 'loader safe.'
Unloading and uncharging
Retention
As a relative newcomer to the world of scatterguns, I found this video quite informative. I'm sure it's a far cry from taking one of his classes, but it helped me better understand how to handle and accessorize a defensive shotgun. Farnam also had some shotgun safety tips that made a lot of sense to me. YMMV