Depends on where you shoot yourself and what round you use. There are birdshot, buckshot, and slug rounds. 00 buckshot would be okay if you shoot yourself in the heart as it would maximize organ damage but you might feel it since having your heart stop isn't necessarily an instant death unless shock takes over immediately. I can't speak for using buckshot on your head, I've never shot buckshot before, only birdshot and slug rounds, so I don't know if it would penetrate the skull as effectively as a slug round would. A slug round would certainly go through your skull and brain and it's a large round so the chances of surviving are low, and if you're in an isolated area it'll be almost impossible to survive it. If you did you'd be unconscious until you eventually did die.