In large skillet, brown bacon until crisp; drain. Cool and crumble. Set aside. Brown ground beef with medium onion; drain. Add together the ground beef and bacon. Mix together baked beans, kidney beans, butter beans, ketchup and brown sugar. Bake in casserole or Dutch oven at 375 degrees for 45 to 60 minutes. Let sit for 15 to 20 minutes before serving. Medium to large casserole: Add 2 medium cans baked beans, 1 can kidney beans and 1 can butter beans. "Crowd size" casserole: Add extra can each type of beans, then extra brown sugar and ketchup to taste.