Bourbon
Bourbon is a bourbon at 43% ABV, used in 3 drinks on this site.

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A tulip-shaped nosing glass of amber bourbon standing beside its bottle
Composition
USDA FoodData Central (SR Legacy) · 174819 — Alcoholic beverage, distilled, whiskey, 86 proof. Public domain. 86 US proof is 43% alcohol by volume by definition; the record's measured ethanol against its measured density gives 42.9%. Bourbon is bottled at 40% and upwards, and 86 proof is the commonest strength above the legal floor. Gluten is not flagged: the spirit is distilled from grain and carries no protein through the still.
Used in these drinks
most firstSubstitutes
Rye — Drier and sharper in the same place bourbon is round and sweet; a sour made with it reads leaner and needs no other adjustment.
A general substitute is a browsing aid rather than a drink-specific claim. Where a particular drink has a substitution worth making, it says so on its own page and recomputes the spec for it.