I am a Blood Hunter (Critical Role class here) with the Sharpshooter and Crossbow Expert feats wielding two hand crossbows. My Crimson Rite allows me to deal an additional 1dx magical damage of some element when I make an attack with a targeted weapon. Sharpshooter simply says that you can add 10 damage to the attack, but it doesn’t specify type. I see a direct comparison to Jeremy Crawford’s ruling on Hunter’s Mark, implying I could choose the damage type of the extra damage. Am I missing some rule that contradicts my assumption?
There’s no official answer, just inferences and DM rulings
The tweet you linked is the closest thing to an official ruling, and Jeremy Crawford’s tweets are not official rulings anymore. However, the tweet is in reference to hunter’s mark, a 1st level spell, rather than to the specific Sharpshooter feat you ask about.
Beyond the tweet
As a DM, I have ruled that you could choose the damage type of the extra damage, for a similar situation (a fighter with the Sharpshooter feat and a bow that dealt piercing damage as well as extra lightning damage). A feat is a fairly heavy opportunity cost, and -5 to an attack roll is a pretty heavy penalty, and it rarely made a difference in my game what type the extra damage was. The few times it mattered, the creature in question had resistances or vulnerabilities that one type of damage would bypass and the other wouldn’t.
Letting the player make the extra damage be the type that would be most useful in that situation didn’t seem to adversely affect balance at the table. In fact, they said it helped them feel like they contributed more when they could actually affect enemies that were resistant to all types of piercing damage, rather than feeling inferior all the time to casters who could plink away with magic missiles or other spells and always affect the enemy. This is of course one table’s experience, with one DM and one group, but it rarely accounted for much of the damage they dealt to enemies.
It mattered more the higher the level they were, since more monsters were resistant to certain damage types, but even then it usually accounted for 10%, at most, of the total damage for the encounter. The player could use it every attack if they wanted to, but tended not to use it much, since -5 was a pretty steep penalty against any enemy with a high AC, and the extra 10 damage was eventually a pretty tiny part of their damage output, especially when they were making multiple attacks per round (see also this analysis of the expected damage output). I think, on average, it was used about once an encounter at most, and there were plenty of encounters that it was not used in.
This experience lets me say that most of the time it doesn’t matter what type the extra damage is. The extra damage is just not that much. Even against resistances, it just meant that the fighter kept up with the casters, and the fighter was barely able to do that anyways in an encounter where no resistances applied.
Ask your DM.
There is no discernible rules a written ruling here. Any answer to this question will be a ruling, not a rule.
In this Q&A, If the attack or spell that the goblin's Fury of the Small trait is applied to deals multiple types of damage, what type is the extra damage?, V2Blast provides some guidance based on commentary by rules developer Jeremy Crawford. V2Blast writes:
As of the release of the 2019 Sage Advice Compendium, there has been no official ruling on this or similar cases. However, official rules designer Jeremy Crawford did provide unofficial guidance on Twitter regarding the hunter's mark spell, which also does extra damage of an unspecified type. He said about the damage type of hunter's mark:
Hunter's mark uses the same damage type as the attack that triggers it. If the attack has more than one damage type, choose one.
He further clarified, in response to a misconception by the other user:
All damage has a type.
So developer's commentary seems to support the player choosing the type.
It may be worth considering how damage types interact with shot placement within the narrative.
The Sharpshooter feat says:
You have mastered ranged weapons and can make shots that others find impossible.
This implies that narratively the Sharpshooter feat is all about shot placement. I can deal 10 extra damage because I am 10 extra good at placing my shots where they can hurt more. As a DM, I would make case-by-case rulings for each damage type in a way that is consistent with this description of the Sharpshooter feat. Essentially, I'm looking to answer the question: Would a particular shot placement amplify the effects of this damage type? If so, I would let the player choose. If not, the +10 is more piercing.
This adds some calculus for the DM, so if you aren't into extra work as a DM, don't worry about it. I won't go through every conceivable damage type and give you my opinion, but I can motivate the idea here narratively with one example.
Suppose we cast tenser's transformation and imbue our attacks with force damage. From a narrative perspective, force damage centered in the torso around internal organs is likely more damaging that force damage hitting you in the ankle (unless you are Achilles). With force damage I would let the player choose to make the +10 damage be force damage.