Well, that's the thing. As far as I've seen right now, it's not removal that kills, it's just tapping it. Even bruising the brain seems to cause death at a 100% rate, from my own testing.
Speaking of, I've been testing for my own mod in development, I figure I should share some of the findings.
Using this
[ITEM_AMMO:ITEM_AMMO_545]
[NAME:5.45x39mm round:5.45x39mm rounds]
[CLASS:545]
[SIZE:50]
[ATTACK:EDGE:40:35000:jab:jabs:NO_SUB:6000]
as my control ammo, I've gotten to a point where the bullet rarely hits vitals or bones (Still working on that...). Often, it'll only pierce the skin. BUT, when it DOES hit a bone, or organ, or anything, it completely destroys it. As well, it only takes one to three hits to cause guaranteed bleed out. I've been holding mock battles with this, and so far, there's a constant 1:1 death ratio. There are zero survivors, because they all take a shot and the bleeding's too intense.
Against armor, it very, very, very, VERY rarely pierces, usually having to wait until it finds an unarmored place, but the results are the same. The battle testing was performed using lines of Amphibian men in cave spider silk robes, using iron ammo and mangrove guns (Gun stats currently identical to crossbow during testing).
I need to perform tests using the buckshot and slug shotgun shells, to see if either of those have a large difference from 5.45 right now.
UPDATE:
One of the first slugs in a robed buck v. slug battle tore apart the brain. Promising. The battle results in a total lose for the buckshot, and 7 lost for slug (About 1/3 of the unit). Within about 20 seconds (At 200FPS), about another 6 or 7 bled out. These tests are being done with complete zero-skill peasant amphibian men.
Let's see how this goes with a full suit of iron armor, otherwise same conditions.
Buckshot v. buckshot. Nearly everyone (Who survived long enough) spent every shell. I note that some toes, fingers, and feet are severed and fly around. Otherwise the rounds deflect off the armor rather than go through. The remaining healthy ones are testing out melee for me while the 3 still alive on the ground are still firing slowly. Considering that the crossbow is basically a small hammer, it should be doing more than constantly being deflected, but whatever. Wiping this group out and starting buck v. slug.
I notice something really odd, Amphibian men are either super fast, or fairly heat resistant, as magma doesn't harm them much. I also note that their bodies remain under the magma, until there's a sudden explosive burst of "boiling blood".
Anyway, enough of that, buck v. slug. Same kinda results, except with less slug survivors. Going through everything, neither go "through" the armor. I'm thinking of testing these as blunt, but the problem is it might not enter them at all at that point. I also noticed, one of the amphibian men died one round after a toe being torn off. Starting to think I should use humans for these tests to make sure if death happens this fast.