Shotguns...now there's a subject close to my heart. Manipulations for them are very weapon dependent (870 techniques won't work with benelli, etc), so learn your gun.
Erick, you know about Hick! I thought I was the only one with too much time on my hands! Truly, his concept is pivotal in teaching us why we should keep things simple(...stupid).
In short, Hick was a researcher who determined that for a given stimulus, we would examine each possible learned solution (milliseconds each one, but it still adds up to time lost) before implementing the correct one. Therefore, train ONE METHOD ONLY (when possible).
The problem with taking this to extremes is that often one manipulation will not solve everything. I had one famous trainer mention that his catch-all pistol clearing-reloading drill would solve all pistol malfunctions. It worked pretty good (if a little slow) until we caused a Feedway Stoppage,.aka "double feed". All he could do was revert to the old way.
The only problem with emergency loading into the magazine is that it takes time. if you've left the action unlocked (stress does silly things to us), you may not be able to get that round into the tube. There's too many possibilities to discuss here, but you get the idea. Make sure your method works in ALL cases otherwise its not better, just different.
With 870s, which is what most of us seem to have on hand, I teach to keep loading the magazine as you need. If you need to do an emergency load (all out of ammo), your first indication will probably be a "click" instead of a bang. Solution - go to the pistol. If you don't have a pistol, and the adversary s close, you won't be able to load anything in time before he shoots you. Transition to medieval tactical principles and club the cr-p out of him with your shotgun. Crude, but effective.
If you will be doing an emergency load, I suggest loading through the port. I also do slug-select drills this way. With the former, remember that you'll be getting the "click" as an indication. This means you action is unlocked (and maybe partially open) which may prevent loading into the magazine.
Open the action (as you run like hell) and load the round on board. Oh, yes, you have to move. Standing and manipulating is not a good idea.
With the slug-select, I don't go in for leaving "dead spaces" in the magazine anymore. I used to follow the logic of leaving space to load the slug and so on, but reality of deployment tells us that buckshot will be the most prevalent round, and slugs relegated to special munitions status. (Unless you always have slugs in it which makes the entire issue moot).
To load the slug with the 870, open the action and simultaneously turn the weapon outboard (ejection port down). this will drop the chambered round and the next round that fed out of the magazine. Now load the slug as you would do an ejection port load. Yes you are dropping two for one, but you are loading the slug because buck is no longer usefull to you.
The Benelli shotguns make all this much easier. Those of you who have them know what I mean.
The final reality check - buckshot will fix 95% of all CQB problems you are likely to face...with ONE SHOT. Transitioning to slugs is a good skill to have on board, but like emergency loading, don't get carried away with it. In several shotgun shootings, some of which involved multiple rounds (both myself as well as other officers) no one ever neded to emergency load their shotgun. I did go to slug one time, but by the time it was done, the bad guy wasn't there to shoot
The one transition that I am aware of, the officer simply dropped the empty shotgun and went to his pistol (very hairy shooting involving multiple BGs, moving cars, etc.)
So, learn your weapon. Learn the best ways to deploy it (meaning simplest way), and make what you've learned reflexive so you don't piss off Mr. Hick who is a cousin of Mr. Murphy.
Gabe Suarez
HALO Group tactical training
http://www.thehalogroup.com