There is a loading of the .410 three inch shotshell that fires five pieces of 00 buckshot. The classic fighting and self defense load for the 12 gauge throws nine pieces. By counting on my fingers I find the .410 is more than half as good. This is an unexpected conclusion but the math is pretty clear.
The .410 is underrated by most as a self defense round. Its wimpish reputation, I think, comes from bird hunters, who can easily ask too much of it without realizing they are doing so. An 11/16 oz. pattern of small shot can reach out only so far. Underestimate the distance and it does indeed seem the little gun is pretty nearly useless.
Buckshot is another story. Five chunks of 00 clipping along at 1200 fps or so seems pretty good! I am speaking here of the use of the .410 shell in shotguns. It has become fashionable to fire it in handguns. I have reservations about this practice. I am concerned over the lesser velocity achievable in a short barrel. My limited experience shooting .410 from a handgun bears out what you would expect; the shot does not hit nearly as hard as when fired from a shotgun. Loadings optimized for the handgun will no doubt help somewhat, but the problem is essentially one of bore volume--it's not possible to cheat at physics.
In addition to more power than some suppose, the .410 cartridge has other appealing qualities. Its recoil is not at all severe. .410 shotguns are in general light and compact. The ammunition is light enough that you can carry a good supply without much trouble.
If you want to learn a great deal about this little cartridge and the guns that shoot it, here is a good place to do it.
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