I've done more research about firearms, and learned that what it really comes down to if you want to know how much damage it will do, is the energy in ft/lbf
A .357 has 583 ft⋅lbf
9mm has 537 ft⋅lbf
.45 ACP has 497 ft⋅lbf
.44 magnum has 1,160 ft⋅lbf
So, when we look at handguns, they're all pretty much in the same range of energy (same damage), except for .44 magnum revolver which is more than twice as powerful than all the other handguns.
Keep in mind though that it depends on which handgun model and ammo you use. You won't get top energy output with any model or ammo. These numbers were taken from wikipedia.
I also looked into black powder firearms a bit more.
And if you load them correct (tight so it shaves of a ring of lead), with a lot of black powder, because more black powder means more energy, up to some point at least. you also must be careful because apparently some black powder gun models can't handle more than a specific amount of energy.
But if you do all above right, you can get them to come up to 486 ft-lbs, which is in the same range of other modern handguns. But if you don't do it right, it can be as low as 343 ft-lbs.
So, the next question is how much energy do we need to achieve 100% success rate?
Success meaning that your brain AND brain stem should be annihilated and you should get knocked out and lose consciousness.
Success is NOT being consciousness and bleeding to death.
Well, it's been said a few times iirc, that suicide by handgun has a statistical success rate of around 50% (i can't remember exactly). This is from some FBI/gov/etc report, I can't remember.
Maybe they were not using the right model of handgun and wrong ammo, and in that case they might only have had around 350 ft/lbf?
Or maybe they aimed it wrong? But aiming is HARD, that's why we want as much energy as we can get, because if we were all masters at aiming, then we wouldn't need much energy. We want to succeed as long as we aim in the general direction. Is it 15% degrees? 30%? 45?%? It's hard to know, and also hard to know how many degrees you're aiming, so we need as much energy as possible.
Maybe the ballistic gelatin tests aren't that useful as I said in another post, because all these weapons, incl .44 magnum and 12 gauge shotguns have more or less the same shock wave in gelatin. But when you shoot on a pig head that results are much different and resemble more the energy values they have.
9mm and .357 do very little damage to a pig head, but a 12 gauge shotgun or .44 magnum does very much damage.
So, because suicide by handgun has a statistical success rate of around 50%, I don't think 9mm, .357, .45 ACP are to be recommended.
The question is if .44 magnum is good enough with its double energy output.
Because a typical 1 oz. (437.5 grain) 2 3/4" Foster shotgun slug (12 gauge) achieves a velocity of approximately 1,560 fps with a muzzle energy of 2,363 ft. lbs. And that's more than double as powerful as a .44 magnum revolver.
Shotguns have 95% success rate, meanwhile handguns have around 50%. But, there are no statistics that I'm aware of that are done only with .44 magnum, so the magnum is put in the same statistics as the other handguns. So, we don't know if the 1.1k energy of a magnum is enough or not. But the 2.3k energy of a shotgun is enough.
The disadvantage with a shotgun is more difficulty to aim, but it's still possible, otherwise it wouldn't have 95% success rate.
Btw, I'm not a gun expert, so please correct me if my research is incorrect.