Spent three days and one night with these guys in a really wonderful shotgun course:
http://www.morrigan-consulting.com
This was not my first firearms course, but my first with the shotgun. I attended with a Remington 870 police magnum equipped with ghost rings, Wilson 2-round extension with sling swivel plate, Speedfeed series III pistol grip stock, 18" bbl with Trijicon front night sight, and a black nylon sling with plenty of slack. If I get a chance, I will take a picture of the shotgun in post-class configuration and post the link.
Well, I had a lot to learn about how to set up a shotgun! I had a few things right, but not all, that is for sure. Here is what I learned:
1. Your shotgun is probably too damn long from trigger face to end of stock (also known as LOP or length of pull). My shotgun was a colossal 14" LOP and was hard to handle. Most are 13.75" out of the box; fine if you are 6'5", but not good for most of us. I am not a small guy but I could not get a good consistent grip on the forearm with a 14" LOP. I put on a shorter stock and got the unit down to a 12.5" LOP. It was like getting a new shotgun. It balances and handles better, especially when my vest is loaded with gear.
2. Reloads on the gun are a good idea. The four or six round units that bolt onto the side of the shotgun are pretty good, but there are other options too. In lieu of relaods on the gun, reloads really quick at hand, like on a bandolier, are a must.
3. Ok, your gun holds six in the tube and one in the chamber. Only load five in the tube and one in the chamber. This way, when you need to switch loads quickly, say from buckshot to slug, you can put the new round in the tube, cycle slide once, and you are ready to go.
4. Sights are a must-have on a defensive shotgun. Inside 15 yards, most people can do a pretty good job with bead sights, but for 50-yard slug shots, you need sights. Ghost ring and rifle sights are fine. Beads are not really that good with slugs past 30 yards.
5. Very few shotguns can keep all the pellets from a 00 buckshot cartridge in a human target, but the pellets can be lethal for much farther. Pattern YOUR load in YOUR shotgun and find out how far you can safely shoot buckshot. Beyond that, switch to slugs or do not shoot. Nearly everyone in my class found that buckshot was suitable from 0-15 yards at the max.
If you want to learn more, take a class. :> These are the most important things I learned from this class. I hope they are helpful.