Abstract: A precision powder hopper comprises a canister for storing particulate material and a rotatable carrier wheel that accurately meters small amounts of the material to a powder out port. The carrier wheel has slots therethourgh that receive definite quantities of material, which is tamped into the carrier wheel slots by a tamper assembly. The tamper assembly includes a deflectable leaf spring that mounts to the same shaft that rotates the powder carrier wheel. A cam and spoke arrangement cause the leaf spring to deflect cyclically in response to rotation of the powder carrier wheel. A cupped spring washer cooperates with the leaf spring to absorb some of the deflection thereof, thereby decreasing the bending stress in the leaf spring and increasing its service life. Powder in the carrier wheel slots is wiped by a novel seal that has at least one circular line contact with the carrier wheel.