Pennsylvania Coal Region Barbecue

These are like Sloppy Joe's, but WAY better, in my opinion.
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Pennsylvania Coal Region Barbecue

1lb ground beef
1 medium onion, chopped
1 1/2 tablespoons white vinegar
1 1/2 tablespoons brown sugar
1 1/2 teaspoons prepared yellow mustard
3/4 cup ketchup
salt
pepper
6 hamburger buns

Crumble the ground beef in a large skillet over medium-high heat. Add onion; cook and stir until meat is no longer pink.
Drain excess grease, and stir in the vinegar, brown sugar, mustard, ketchup, salt and pepper. Simmer over medium heat for about 15 minutes. Serve on buns.