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Let’s start with Infusion. It technically does what it says, it converts damage, 8% per point allocated skill point. But…
On non-elemental guns, you lose 8% non-elemental gun damage but gain the same amount as shock/corrosive/fire elemental damage. This can be favourable if you attune yourself to the element an enemy is weak against (fire for flesh, corrosive for armour and shock for shields) because those elements get multiplied as shown on the chart above and also benefit from Amara’s Tempest skill.
Cryo and Radiation guns fall in between non-elemental and elemental corrosive, fire and shock guns. They have more average/consistent multipliers then the other three elements across the three defence types but are slightly more specialised than non-elemental guns. With those two elements Infusion can make sense if you run them exclusively. But as soon as you also run the other three elements Infusion would be detrimental.
If you’re using corrosive, fire and shock elemental guns your almost always better off not using Infusion and instead switch guns depending on weaknesses. 100% corrosive damage against armoured targets is always better than 60% corrosive (with 5/5 Infusion) and a bit of additional shock or fire damage that’s significantly reduced by the multiplier shown on the chart.
You could argue that this can be countered by just switching elements in the skill tree to have both gun and Infusion set to the ideal element. That’s true but that has also two downsides:
- Both the base elemental damage and the conversion from Infusion are calculated separately by the engine and therefore they apply DOTs individually. The base DOT that is usually stronger gets applied first and the DOT from Infusion afterwards. But when both elements are the same the weaker Infusion DOT will override the stronger base DOT. Not a big deal for the most part since DOTs are usually weaker than the front-loaded direct elemental gun damage.
- You invest valuable skill points in order to get exactly the same result as if you’d just ignore Infusion.
IMO the only reason to use Infusion on those elemental guns is if you want to stick to a certain gun/element because you like that gun/element or you don’t want to switch weapons. But you have to keep in mind that you’ll lose damage/DPS and will need more ammo to get the same result.
It’s also important to mention that DOT damage is not only tied to elemental damage and its modifiers but also directly to gun damage. If you increase gun damage you also increase DOT damage. Some guns have higher special multipliers for the Gun Damage to DOT Damage conversion but the same rule applies here as well: when increasing gun damage on those guns with a special multiplier you also increase the DOT relative to the special multiplier. By splitting damage via Infusion you’ll always end up with weaker DOTs.
Here are some screenshots for comparison to show the difference and make it clearer what I described above. I used a corrosive weapon on an armoured target to represent the ideal case. First the damage without Infusion. The 408 is a DOT tick that can be ignored.
And now with 5/5 Infusion and attuned to Shock. Everything else stayed the same.
In comparison, 40% or 444 less corrosive damage was dealt (removed) while the shock conversion from Infusion added just 165 shock damage.
In this scenario, if the target would also have a shield I’d deal more damage to the shield but way less to the armour part. If you’re facing shielded enemies regularly and don’t have any other easily accessible source for shock damage (e.g. grenade) one point in Infusion is usually enough to strip shields quickly. That way you can retain the majority of base elemental damage. Or you could just use a radiation gun which makes quick work with both shields and health bars. That way you could spend those skill points elsewhere. For beefy boss shields, you want to carry a shock weapon anyway.
[GunDamage] * ( [GunElementMultiplier] * [InfusionMultiplier1] + [AttunedElementMultiplier] * [InfusionMultiplier2] ) = [ResultingDamage]
[InfusionMultiplier1] = 1 – 0.08 * [InfusionRank]
[InfusionMultiplier2] = 0.08 * [InfusionRank]
Non-elemental gun, 500 base damage, attuned to fire, flesh target, TVHM, Infusion 5/5:
500 * ( 1 * 0.6 + 1.75 * 0.4 ) = 650
Without Infusion it would be only 500 damage, not accounting for Mayhem modifiers, elemental damage bonuses, etc.
Now do the same thing for an elemental gun but with dual-element (having both gun and Infusion set to the same element doesn’t make any sense as described above).
Shock gun, 400 base damage, attuned to fire, flesh target, TVHM, Infusion 5/5:
400 * ( 0.65 * 0.6 + 1.75 * 0.4 ) = 436
For comparison, by using a fire gun with 400 base damage, without Infusion and on a fleshy target you’d deal:
400 * 1.75 = 700
This skill doesn’t convert damage but you’ll get 18% bonus elemental damage on top of the damage you’re normally dealing with your gun. In this case, it doesn’t matter that much (compared to Infusion) what type of element your gun has by default, it’s always 18% of your gun damage that gets multiplied. Having both gun and elemental damage bonuses increases its potential significantly due to them interacting multiplicatively with each other.
It’s best used when you attune yourself to the element an enemy is weak against. While mobbing it’s great for stripping shields (attuned to shock) if you don’t have any other source of shock or radiation damage. For bosses, you should switch to fire/corrosive unless the boss has a beefy shield.
[GunDamage] * ( [GunElementMultiplier] + [ExpressionMultiplier] * [AttunedElementMultiplier] ) = [ResultingDamage]
Non-elemental gun, 500 base damage, attuned to fire, flesh target, TVHM:
500 * ( 1 + 0.18 * 1.75 ) = 657.5
Fire gun, 400 base damage, attuned to fire, flesh target, TVHM:
400 * ( 1,75 + 0.18 * 1.75 ) = 826
So far I can say that it’s always beneficial for non-elemental guns. And when using a non-favourable gun element (shock on fleshy targets) with Infusion the additional damage from Forceful Expression outweighs the loss in damage to some degree but it’s still worse than just using the correct gun element respective to an enemy weakness.
I haven’t yet figured out how the combined formula for both skills looks like. I’ll update the thread in case that changes. If you think you know how it works send me your data and I’ll include it.
Sustainment uses the default element of your gun and 100% of its damage for its calculations. That means if you’re using a non-elemental gun with Infusion you won’t get any life steal. But you get the full amount with elemental ones, even when using Infusion on top of that. Neither Infusion nor Forceful Expression make a difference when it comes to life steal from Sustainment.