Answer: don’t let someone shoot you with buckshot at 50 yards. If you do, you’re gonna have a bad day.
Side answer: 00 and 000 buck is where it’s at.
Bonus side answer: the size of the shell isn’t relevant, just the speed and size of the projectiles. Because those are largely gauge-independent, the only cost analysis you really have to take into account is number of pellets. While 20-gauge is often overlooked for self-defense, it’s clear that if you can get a good pattern with it and get hits on target, those pellets are gonna be effective.
Gratuitous side answer: shotguns rule.
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