So I'm about halfway through Stressfire II: Advanced Combat Shotgun by Massad Ayoob, and so far, I'm liking it. I haven't read Stressfire I yet, but it's on the list. II is all about shotguns though, and I is only referred to in passing once or twice.
Like I said, I'm about halfway through it right now, but the book is set up with the first half being about gear and ammo and the various hard technical aspects, and the second half concentrates on technique, so it's a good spot to pause, and I need some content anyway. One of the things I'm liking is it seems that Mr. Ayoob's thoughts on semi versus pump seem to mirror my previous, less educated thoughts on the subject. The biggest thing being where I only have my mediocre common sense and limited personal experience, he has a massive background and can dig up the numbers to back it up. He mentions that one department he worked with switched from pump action Ithicas to Benelli autos, and the qual scores went through the roof, and has noticed it in other places as well. (pg47) As for other action types, "two shot guns are for users with two digit IQs."
One word of caution, Chapter 3 is not for the squeamish. On the other hand, if you want some good looks at what you can accomplish with a shotgun against human flesh, you won't be disappointed.
He also goes into the various chamberings available, and of course challenging the proliferation of the 12 gauge. Turns out a 20 gauge loaded with #3 buck is damn impressive, 20 some projectiles, similar velocity to the same out of a 12, yet lower recoil. (Downside being that your 000, 00, and #1 balls don't stack well in a 20 gauge shell.) .410, conversely, even with a slug, gives you at best the same terminal ballistics as a decent .44mag or .45acp, so why hinder yourself with a long gun to get pistol effects? (Let alone out of a handgun... but that's another subject all on it's own.)
The book is getting a little dated, the newest coolest semi talked about is the Benelli Super 90, albeit with much praise, but I can't help but wonder how he would compare it to the M4 (I'm sure there's an article out there somewhere.) And nothing whatsoever about the newest Mossbergs (no semi's from them at all at the time of writing.)