3 inch shells are magnum loads. Newton’s second law: “for every action there is an equal and opposite reaction.” The recoil will kick you like a mule and make it harder to stay on target. 3 inch shells are for things like duck hunting. 2 1/2 inch shells are fine for HD.
Birdshot is effective point blank but if you’re defending yourself in winter, the intruder is heavily clothed, etc, not so good. You need immediate penetration. Center mass kind of thing.
00 buck is preferred by a lot of people but in an apartment building or if there are other people in your house, the buckshot will not stop at the drywall. It penetrates drywall with enough energy to kill whatever is on the other side.
My main home defense is a handgun with light/laser. But I also have a shotgun with #4 buckshot. Note: not #4 duck hunting shells as that’s different.
But if I hear something shatter in the night, it’s my 45 ACP with the light/laser. And my electronic ear muffs if I have time and presence of mind. Long guns are a worst case scenario thing.
That’s why I keep a pistol handy
9mm but I have a couple of new .45s (from last year that is)