I use chuck & sirloin steak & roasts when they're on sale. Trim all hard fat. Cut into 3/4" cubes, then into the freezer to firm up a bit. Then into the Cuisinart in small batches so the meat is small pebble size. Then spread it out onto a baking sheet, pick out any gristle, pour a small amount of melted butter or bacon fat on top, season, then gently shape into a large patty using a form.
These will be incredibly tender patties so care must be used when cooking & turning.
A true 'melt-in-your-mouth' burger....