I first saw Aguila 1 ¾-inch 12 gauge shells at SHOT a couple of years ago. They are, for want of a better word, cute. My first thought was, "these would make great cufflinks." My second was to wonder how many would fit into the magazine of a pump gun.
Apparently a lot of other people wondered the same thing -- about mag capacity, not the cufflink thing -- because the web is full of videos of people stuffing Aguila shotshells into their guns. They come in a 5/8-ounce load of 7 ½ shot at 1,150 fps, a buckshot load containing 11 pellets of 4 buck, and a 7/8-ounce slug at around 1,200 fps. You can fit a lot of them into a shotgun. I believe the record is 29, into one of those bullpup riot guns with two magazine tubes. However, the short cases don't cycle well in some pumps as the short hulls double-feed or sometimes fall through some carriers and out of the gun.
Apparently, the Winchester 1300 is one gun in which they work very well. Notice how the muzzle of the 870 in the video hardly rises and the gun hardly seems to move back against the shooter's shoulder. They would make a good low-recoil home defense load in a double gun, I imagine, since home defense encounters take place at very short range where high velocity and big pellets wouldn't make an intruder any more dead. The 5/8-ounce loads of 7 1/2s would make a nice training load, too.
Short shells like these are really at their best in break-action guns. They are nothing new: the English loaded 2-inch 12 gauge shells for women and children to shoot. Those also don't work well in most pumps or semiautos; I have tried. If you really want to shoot ultra light ammo, the best thing to do is handload your own in 2 ¾-inch hulls. I have done that with 5/8-ounce payloads just to see if I could.
Meanwhile, these are novel, and if people buy them to see how many fit into a gun but discover the joy of low recoil instead, then I guess they are a good thing. The best part of the many videos I have seen is the look of delight on people's faces after they shoot a shotgun and it doesn't hurt. It is exactly the opposite of the face I made after shooting 3 ½-inch shells in the Gun Nuts TV video. (And no, I don't know why Dave is smiling in that one.)