Basically, I have an actor that I wish to add a full-face helmet too (A Combine Soldier from the CMB Revisited Mod), I want to create a helmet that covers the entire head, and at the same time stops bullets from hitting his head, but whenever I set the mass of the helmet to zero, bullets pass right through it, and when I set it to more than zero, (basically any number), it stops bullets but when broken, the actor dies as well. Is there any way to fix this?

This means the JointStiffness variable on your helmet is too high.

look for that variable in the code and play around with it. Be careful though, set it too high and scary things happen when the helmet breaks.

What happens when the jointstiffness is too low, and what does jointstiffness do for legs and arms?

I tried what you said, and the combine's head no longer explodes upon helmet termination, but now it just falls over dead instead, head intact.

What's the BreakWound for the helmet?

The entire thing for the helmet is:

AddEffect = Attachable
PresetName = Combine Hack Helmet Elite
Mass = 1
Sharpness = 0
HitsMOs = 1
GetsHitByMOs = 1
SpriteFile = ContentFile
FilePath = CMB.rte\Sprites\Actors\EliteHead.bmp
FrameCount = 1
SpriteOffset = Vector
X = -2
Y = -7
AngularVel = 6
EntryWound = None
ExitWound = None
AtomGroup = AtomGroup
AutoGenerate = 1
Material = Material
CopyOf = Military Stuff
Resolution = 4
Depth = 1
DeepCheck = 1
JointStrength = 100
JointStiffness = 0.1
BreakWound = AEmitter
CopyOf = Wound Flesh Body
JointOffset = Vector
X = 0
Y = 0
DrawAfterParent = 1
GibImpulseLimit = 99999
GibWoundLimit = 18
AddGib = Gib
GibParticle = MOSRotating
CopyOf = Gib Metal Rusty Small A
Offset = Vector
X = 1
Y = 4.5
AddGib = Gib
GibParticle = MOSParticle
CopyOf = Gib Metal Grey Tiny A
Offset = Vector
X = -1
Y = -7.5
AddGib = Gib
GibParticle = MOSParticle
CopyOf = Gib Military Micro A
Offset = Vector
X = 0.5
Y = -8
AddGib = Gib
GibParticle = MOSParticle
CopyOf = Gib Military Micro A
Offset = Vector
X = 1.5
Y = -1

Ah, I fixed the issue. I simply set the breakwound to "Null Emitter". Thanks for your help!