Do the benefits of oil of sharpness stack with those of +1/2/3 magic ammunition?
I'm really just curious whether these also stack as +X ammo does with a +3 bow, or if there's a point at which things stop stacking.
Do the benefits of oil of sharpness stack with those of +1/2/3 magic ammunition?
I'm really just curious whether these also stack as +X ammo does with a +3 bow, or if there's a point at which things stop stacking.
According to the official rulings in the Sage Advice Compendium - page 18:
In general, bonuses stack, unless they’re from the same spell
Also, in the DMG - page 252:
When two or more game features have the same name, only the effects of one of them — the most potent one — apply while the durations of the effects overlap. [...] Game features include spells, class features, feats, racial traits, monster abilities, and magic items.
These are items but they do not have the same name so this rule does not apply.
There is no specific rule on the oil of sharpness or Weapon +3 or Ammunition +3 that would override this, so the bonuses do stack.
Oil of Sharpness states:
the coated item is magical and has a +3 bonus to attack and damage rolls.
If I coat a piece of ammunition in the oil, it has a +3 bonus. The oil does not add a +3 bonus.
If I coat ammunition +3 in the oil, then claim the ammunition has a +6 bonus, my claim contradicts the rules for Oil of Sharpness, which state my ammunition has a +3 bonus.
Here's how it would play out if I was DMing:
Player: I coat my +3 arrow in oil of sharpness, now it has a +6 bonus.
DM: Let me check that, what does oil of sharpness say?
Player: "the coated item is magical and has a +3 bonus"
DM: Then we'll go with what it says, it "has a +3 bonus".
Yes, bonuses from different sources stack. There can be more than one bonus for something - there are plenty of such examples in the game.
There can be a +3 bonus from one source and +3 bonus from a different source. Being from different sources, those bonuses stack.
As an additional argument, consider that Oil of Sharpness and a +3 weapons are both Very Rare items. The former is a single-use item, lasts only for 1 hour, and requires a minute to apply. This makes that +3 weapons much, much better. For that reason as well I would assume they were intended to stack.