In north america you would be hard pressed to find anything that you could not kill with a rifled slug. I was raised on shotguns and have thirty years in a police car where the weapon of choice is a .12 ga.
an assortment of ammo is all you need to make this gun "kind of fit" any situation. However if you are talking long term self defense you have to have a gun that will be with you when you need it. That is why coppers carry side arms. There are times when you just don't have the .12 ga with you.
I carry both autos and revolvers as the situation calls for them. For long term protection you would be hard pressed to replace a revolver with at least a .357 round.
I know this will start an argument but I have spent time in the woods and I have never had a misfeed in my revolvers. Every auto I have ever had has misfed at least once. I am not talking cheap guns. 1911's , sigs and berettas.
Most of the misfeeds have been ammo related and a few have been grip errors. But still they were there.
An auto relys on a magazine that is not part of the weapon it is an accilary piece that is often subjected to different stresses because it is not in the gun. Revolvers misfire and the next round is comming around. The Mag in a revolver is a part of the gun.
With modern reloaders you can come pretty close to loading as fast as a mag change with practice. However most copper confrontations use to be 2. something rounds.
Now we train different and the guys tend to throw all their shit downrange as quick as they can.
My duty right now is in soft clothing and I find that a .44 special is all that I really need. I don't feel the burning need to buy anything but a Charter Bulldog.
when I was doing drug raids I liked my Sig .45 and the 1911 because I had firepower to provide "distraction fire " in order to move guys out under cover.
I liked the fact that if we started recieving fire as we were coming up on a clan lab in the country that I could send heavy lead down range. I also carried an SKS that I had taken off a drug dealer and found this gun very accurate and idiot proof. I have fired at least 1,500 round through that bastard and never had a jam, when I stopped working drugs I gave it to my replacement and he is proud to have it.
I also had a M1 Carbine that I used because it did not look like a copper gun and I could pretty much leave it in my car and the bad guys just thought I was a turd. Bad bullet for a carbine but it must have been a great SMG round.
I also carried at times a single shot 45/70 because it would bust propane tanks and all the labs we were involved in relied on propane tanks to hold anhydrous ammonia.
A .357 will bust a twenty pound tank pretty reliable but your .40's and .45's would consistantly bounce off. In fact a rifled slug frequently bounced off of them if they were full.
Just a ramble about some of the guns I have carried in the field.