Marinate drumsticks in buttermilk, Worcestershire, and 1 teaspoon salt in refrigerator 4 to 12 hours.
Mix flour, black pepper, mustard powder, garlic powder, and remaining salt in a broad bowl.
Dredge drumsticks in flour; dip briefly back into buttermilk. Pack on a second flour coat.
Rest coated chicken 15 minutes while heating 1 1/2 inches oil to 325°F.
Fry six drumsticks at a time, 14 to 16 minutes, turning every 3 minutes and maintaining oil at 315°F to 325°F.
Probe thickest part without touching bone; remove only at or above 165°F.
Drain on a rack 10 minutes. Return oil to 325°F before frying second batch.