So I had to really think about lethality of different classes of firearms- penetration is not the only mechanism,..
I believe I understand your intent, but I think "lethality" is not the proper term to use. First off, because there is no deader than dead. There is no dead++.
Second, when speaking in terms of self defense, the objective is not to kill, or not kill, the objective is to make the attack STOP.
It's a fine point of language, but language does matter AFTER the shooting is over. We can discuss this in depth, but that's a bit off topic for this thread.
here's a point, somewhat relevant to .410 pistols (and revolvers ARE pistols, too) and its the velocity of the buckshot (and all shot). Shot shells are rarely loaded to velocities above 1300fps. One reason is that this is the approximate max speed obtainable with black powder, so keeping speed (and pressure) in this range means that old guns can use the ammo too. But the practical part of the reason is that at velocities above 1300fps, patterns degrade.
Modern guns and ammo can produce speeds much higher but the don't, with shot loads, because even though higher speed means more energy, when the pattern goes to hell, the effectiveness of the shotgun decreases.
SO, at "best" we start with buckshot loaded to do approx. 1300fps from a long gun barrel, and then put it in a 2-3" "defensive" pistol barrel, so 800ish fps is not an unreasonable number.
Now, compare some different ammo and you'll find some doing about the same from the really short barrels, I would expect roughly similar speed from standard .45 colt. There are more powerful .45 Colt loads but I doubt the Judge/Governor can handle them.
Watching the blocks of jello, they are wiggling like they are being kicked with a boot on each shot. That’s not quite what a .45 Colt slug would do?
There are .45 Colt loads that won't make that jello block just wiggle, there are some that will blow it off the table. But, again, I don't think you can shoot THOSE from a .45/410 pistol.
What I am most curious about, at the moment, is what does one get for speed and energy shooting .410 slugs from one of the short barrel pistols???
I'm looking at a box of Win 3" slugs and it says the speed is 1800fps. No doubt that's from a long (at least 18") barrel, but what's it going to be from a 2.5 or 3" tube??? I think it ought to still be significantly more than the buckshot.
At "point blank" range, shot strikes essentially as a single mass, so I think its fair to compare that against a single slug. IF that's the case (I'm willing to listen to arguments) wouldn't it make more sense to use the most powerful round practical??
Especially if you include "penetration barriers" such as heavy clothes, leather "armor", the attackers arm, or an angle where the vitals are more difficult to reach.
Just my current opinion, and I'm willing to change it, IF you can convince me, but I would rather have more "punch" and less spread if my personal posterior was at risk.