Combine grape jelly and chili sauce in the bottom of a crock-pot. Stir until mostly combined.
Add the mustard and horseradish if using and stir into sauce.
Put all of the meatballs into the crock-pot and combine with the sauce, make sure all of them are coated.
Cook on high heat for approximately 2 hours, stirring every 30 minutes.
Serve with cocktail forks or skewers
Notes
This is enough sauce for 36-48 meatballs. The cooking instructions are when using a crockpot on high heat. If using medium heat, cook an additional hour.