j) The racking of a pump-action shotgun can be unreliable if the user is under stress.
a) If you need the spread of a shotgun to hit your mark in any context, you suck ass, and probably shouldn't be carrying a gun in the first place. Learn how to properly aim and shoot a rifle instead.
3. Self defence innacity
Many of the same things I've mentioned before apply here, but some more than others.
a) Because of their general length, they are pretty much garbage inside cramped spaces like houses.
b) Their lack of ammo capacity is even more important here, as it is likely that you have to defend yourself against other firearms. Suppressive fire is a thing in this context, and that's something you just cannot do effectively with one shotgun.
While shotguns can be very effective in some contexts, they are not ideal in the vast majority of them because of all their shortcomings. There's a reason for them not being very popular with most military and law enforcement agencies around the world. They are weapons that have very specific roles.
So, seeing that this is /out/, and not /k/, I would tell you to carry a large caliber pistol, my own recommendation being a Glock 20 chambered in 10mm Auto, for that rapid fire, fast reload bear medicine, or a fairly short, semi-automatic rifle chambered in something like 7.62x51mm NATO or .30-06.
My reasoning for this, is that the sole act of carrying ammo for such weapons is just way more practical, as you can go out with one magazine in your gun, and just have a couple of extra magazines with you, and you don't even have to load each individual cartridge.
Of course, none of this will hopefully never be a factor, but as with weapons in general, it's not something you need until you need it.