Preheat broiler. In a large mixing bowl combine the bread, onion, ketchup, worcestershire sauce, mustard, horseradish, garlic powder, and chili powder and mix until well blended.
With clean hands add ground beef and blend gently until combined being careful to not overwork the meat mixture. Shape into six (3-inch) burgers and place them on a ungreased jelly roll pan or cookie sheet.
Broil the burgers four inches away from the heat source approximately four minutes per side or until desired doneness. Place cooked burgers on hamburger buns and serve immediately.