
You have perfected the creation of poisons, their use, and developed a tolerance against them. You gain the following benefits:
- Increase your Dexterity or Intelligence score by 1, to a maximum of 20.
- You gain proficiency with a poisoner's kit, and you add double your proficiency bonus to checks you make with it.
- You can apply a poison to one slashing or piercing weapon or up to three pieces of ammunition as a bonus action.
- You have advantage on saving throws against poison.

If it were one piece of ammunition, I would upvote, but three is both too much and feels wonky/cheesy.
3 pieces of ammunition is the standard for poisoning ammunition.
That's the standard in official rulesets