.223/5.56mm JHP penetrates *less* than 00 buckshot, hence is less likely to completely penetrate than 00 buck.
Where does this information come from? Because I've never understood how an individual 00 pellet, which has less energy than a .380 round, is going to penetrate "more" than a rifle that has more energy than a .44 magnum (and I know some debate that issue but the muzzle energy formulas give the nod to the .223). I've shot lots and lots of guns in my life and this goes contrary to everything I've ever seen. A .223 round that expands perfectly may not penetrate much more than a 12 ga. but in building materials the 12 ga. buckshot load has been shown to not penetrate nowhere near what some .223 rounds do on the Box O' Truth website. Buckshot didn't penetrate even 8 sheets of sheetrock while the .223 round tested went through 12 sheets of plywood and kept right on going. They never got it to stop in their tests. I'm sure it stops somewhere but they limited the tests to the materials they used to test handguns and shotguns.
A .223 bullet is far heavier than a 00 buckshot pellet and it travels at a far higher speed. The combined capability of the buckshot round is what makes it effective against humans. But it also has a round shape which is about as bad as it can get for resistance. The .223/5.56 round is a Spitzer shaped bullet designed for penetration. Of course it's also designed to expand on impact but from what I understand only the very best designs work a high consistency rate for expansion.
Basically I've shot things for 50 years using shotguns, rifles, handguns, machine guns, and air guns. I know what I've seen. I've seen 2.23 rounds go through solid rock at 500 yards (about 3" of sandstone). I don't see how a shell filled with buckshot is going to do anything like that even at short distances. And of course buckshot does not carry 500 yards if it would happen to miss the target and fly out an open door or window or through a thin wall with sheetrock, insulation and vinyl siding as the only objects that must be penetrated. A .223 round can go right through a wall like that and travel a long distance and still do damage. I do not understand what some think a 2.23 type round is safer for not hitting things far downrange or even across the street close. For one thing buckshot will spread a good bit just going across the street so the chances of a person being hit by several pellets is low. And yes I have tested buckshot to see exactly how far it spreads at distances. Even the best designed shells spread considerably after 40 yards. I've done tests with cardboard at various distances with various loads. I did it to see what spread the least. But I learned that no buckshot loads stay together for a long time. So at most a person may be hit by half the 00 pellets at 50 yards especially after those pellets have penetrated a wall. They will lose a good bit of potency just penetrating the wall, they will spread out more if they penetrate a wall and they start out with far less energy per pellet than a single .223 type round.
I understand wanting to have multiple rounds available and I understand that a semi-auto is better than a pump shotgun but shotguns come in automatic form too. I use a pump because of reliability and because I've been shooting shotguns for 51 years and I have a pretty good idea how to make one work quickly. That may not be true for everyone of course.
There are no doubt benefits to each choice. But for me the choice is pretty obvious. I'll take a 12 ga. pump shotgun with a large tube and a side saddle round carrier. It may not fire as much as an AR but it will fire a lot of pellets shooting 8 or 9 at a time. And followup shots can be done quickly if you have practiced enough. I understand the risks of short stroking a pump gun in a stress filled situation but I've seen AR's jam too often to not worry about whether it will happen because of a stress reaction while shooting them. The body does things different under stress and that applies to shotguns and AR's.
I'd really like to see the data on this that people cite. I've seen some tests but the ones I've seen compared .223 rounds to shotgun slugs. Well that's not a fair comparison. I use slugs for bears. I use buckshot for intruders or I would if I ever actually had one.
So if you have a link to a study I'd like to see it to see the testing and what the reasoning is.