Travis Pike has a good article on the problems with a magazine-fed shotgun, and he makes the case that they’re just not worth it.
I agree. Based on what I’ve seen in my classes, the ten (or so) rounds you can stuff into a 12 gauge magazine don’t offer you much advantage over a tube-fed gun, especially in a defensive situation. Most tactical shotguns hold at least seven rounds in their tube, not all that much less than the ten rounds in a magazine. We’re not talking about the difference between six rounds in a revolver and the 17 rounds in a Glock G17 here, we’re talking three rounds. More than that, storing more than one spare mag on your belt (if you can find belt pouches to accommodate a 12 gauge magazine), is theoretical at best. All of a sudden, having 25 loose shells in a dump pouch on your belt, ready to be loaded into your gun starts to make a lot of sense.
And then there’s problem of the actual reload. Let’s say you run dry with a tube-fed gun. If your gun is set up properly, with a receiver-mounted shell carrier, you reach around, snag a shell, drop it into the ejection port and close the action. Loading your gun this way means your hands have to move 3-4 inches at most as you get your gun back into action.
With a magazine fed gun, though, it’s a matter of hitting the mag release, then reaching down to your mag pouch, grabbing a magazine, slamming it home and closing the action. Sounds easy, and it’s something we do all the time with a semi-automatic pistol or rifle. However, your hands have to move upwards of a yard or more to get to the spare magazine and slam it home, which takes much more time to accomplish. Yes, when you do that, you have ten rounds ready to go, rather than one, but during all that time, you’re staring at your opponent with an unloaded gun.
And then there’s the matter of the bullpup, box-fed scattergun. The fact of the matter is, it takes less time to reload a tube-fed gun to full from your receiver and a dump pouch than it does to switch hands and fumble around with a reload when using a bullpup gun.
I think a lot of the passion for box-fed scatterguns come from 3 Gun (where they are actually useful) and the desire to have a common manual of arms across pistol, rifle and shotgun. Let shotguns be shotguns, and let rifles be rifles, and don’t try to confuse one with the other.