Marinate the drumsticks with the buttermilk, Worcestershire and 1 teaspoon salt for 4 to 12 hours in the refrigerator.
Mix the flour, black pepper, mustard powder, garlic powder and remaining salt in a broad bowl.
Dredge each drumstick in flour, dip it quickly back in the buttermilk and pack on a second coat of flour.
Rest the coated chicken for 15 minutes while heating 1 1/2 inches oil to 325°F.
Fry six drumsticks at a time for 14 to 16 minutes, turning every 3 minutes and adjusting the heat to stay between 315°F and 325°F.
Probe the thickest part without touching bone and remove the drumsticks only when they register at least 165°F.
Drain on a rack for 10 minutes and let the oil return to 325°F before frying the second batch.