I'm working on making a boss character, but I've noticed that if shot in the head sometimes he will instantly die. I've already made him quite resistant to gunfire, yet sometimes he literally dies from 80 health and I can't figure out why. Any ideas?

He has a mask attachment that serves as armor for his face, if it helps any. He also happens to be trying to crawl every time he dies from the magical critical hit bullet.

Is the gibimpulselimit of the head high enough?

GibImpulseLimit, GibWoundLimit, LifeTime, JointStrength, JointStiffness, etc.

Check those.
Also, if you didn't know, the material it has determines how "strong" it is versus flying pixels.

JointStrength is currently 5000, JointStiffness is 0, GibImpulseLimit is 20000, GibWoundLimit is 50, and the material is Mega Metal.

I've seen him die at 80 health from a fair distance after being shot by a dummy pistol and also by a coalition assault rifle.

Make JointStiffness 0.5.

Sure thing.

What exactly will it do? By my understanding it determines how much impulse the parent will inherit from the child. Does that mean that the character's body will take 50% of the impulse the head does?

Does the head have any attachables on it? I've had many problems with heads becoming fragile when other objects are attached to them. Try reducing the weight of any attachables, that usually seems to fix the problem. Also, look for duplicate code lines. Once, I made an actor with a GibWoundLimit of 500, but it kept dying when shot with the weakest weapons. I spent hours trying to figure out why, until I noticed that in the end of the code, there was a line with GibWoundLimit = 1.

Ahaha, I've had those kinds of moments before. Those moments where you're not sure whether to be proud of yourself or to kick yourself, lol.

The character is actually wearing a breakable mask that covers up all of his face. The weight may be an issue, I just noticed that its mass is about a third of that of the character's head. I'll test that out, thanks.