In two stockpots over medium heat, cook and stir beef and onions until meat is no longer pink; drain.
Stir in the ketchup, Worcestershire sauce, brown sugar, mustard, vinegar and chili powder. Bring to a boil. Reduce heat; simmer, uncovered, for 1 hour to allow flavors to blend. Spoon 1/3 cup onto each bun. Yield: 96 servings.