The invention relates to a timepiece barrel (1) pivotably mounted between a bottom plate (9) and a bridge (5) and comprising at least one spring (7) housed between a pivotable drum (6) and a cover (8) and engaged between said drum (6), at the outer end thereof, and a shaft (3) that is pivotably attached to a ratchet (2) about a pivot axis (D), at the inner end thereof. Said barrel (1) comprises a one-piece subassembly (10), which is coaxial with said shaft (3) and which combines said shaft (3) and a core (4) provided with a collar (17) that limits the axial play of said drum (6), said collar supporting a means (42) for pivoting said ratchet (2), which is axially free in the direction of said pivot axis (D).