Agreed AE most burn victims don't die from blood loose or other damage per say but from exposure or shock and these take hours if not longer to happen.
Certainly you can kill someone in a variety of strange way but if your weapon is a projectile weapon and you are attempting to kill the target quickly then I think most of the evidence point thusly:
First and foremost you must hit your target, this is by far the most import thing. A hit very accurate hit from a 22 short is infinitely more effective than a miss with a 50BMG.
Second projectile performance, this being that the projectile achieves enough damage to the target that it will be quickly lethal. This mean the projectile must destroying the central nervous system by direct attack or destroying the blood supply or the oxygen supply to the brain.
That said you could certainly kill someone with zero penetration projectiles. If I could shoot and object the size of a door at a human size target and hit them at a high velocity It could through pure concussion smash them to death. This would damage the brain as the head is smashed into the flat object, if the impact was hard enough it would also damage internal organs. The problem here is large flat door like projectiles is that they SUCK as projectiles. The desire to have the projectile travel long distances accurately dictates the type of lethality they will be good at. A projectile that is good at penetrating air will with also be a better at penetrating a target then trying to act like a mace.
The only effective Zero penetration projectile weapon I can think of is using blunt tipped arrows for small game hunting but then again here we have a projectile (the arrow) that weights on the order of 3% the body mass of the target. Figuring a blunt tipped arrows weight about 400-450 grains and a rabbit is about 2 lbs. To get similar for human target you would need 5-6 pound projectiles. Death is by blunt trauma usually a blow to the head or ribs but even here the rabbits are not always dead simply knocked senseless giving the hunter time to retrieve the rabbit and dispatch it. Conversely a 180 grain bullet weight on the order of 0.01% of a human target.
The flamer now there’s another near zero penetration weapon but they are hard to conceal under a long coat and finding and effective flash suppressor is really tuff.
more rambling from:
mcb