A little while ago, I had done some research on Impact, and found out something very interesting. The skill increased a field called "bullet damage". What made this interesting is that this field was actually different from the weapon's damage, making the damage increase multiplicative (and not additive). This is interesting by end game, where proficiencies already give you +50% damage, your mod already gives you +80% damage, it is nice to have a fresh field to pump up.
I have put further research into the subject:
It would appear brick's Revenge is also affected. Most probably a few other skills also have this unique property (My shortlist would be Enforcer/High Velocity, and Relentless, but I also need to check Caliber and Trespass).
There are two easy way to check:
- By looking at your "Damage" in the debug console. If the field is un-affected by the skill, the it is the bullet damage that is increased.
- By firing at a baby spiderant, and writing down the damage. Calculate if the damage differences with/without the skill is additive/multiplicative.
So appart from this behavior, what else is interesting? The answer lies in the question: Why aren't rockets un-affected? From the game mechanics' point of view, a rocket is just an elemental bullet that moves very very slow...
And that's when it hit me: A weapon's "proc" damage is not affected by bullet damage: The damage of the elemental effect is calculated from the weapon's damage. Because rockets are actually 0% bullet damage and 100% elemental damage, they are un-affected.
How does this influence your game play? If you are using DoT procs, it doesn't, since it is the DoT that affects damage anyways. If you are using explosive damage though: the Ogre, Cobra, then be aware that the above skills will have very little effect on the weapons.
TL;DR: Some skills increase a field called "Bullet Damage". This effect does not stack with damage, but multiplies with damage. The increased bullet damage has no effect on elemental procs/effects (including rockets).