In a bowl, combine the flour, baking powder, baking soda, and salt; cut in shortening until the mixture resembles coarse crumbs. Stir in buttermilk; knead dough gently. Roll out to 1/2" thickness. Cut with a 2-1/2" biscuit cutter and place on a lightly greased baking sheet. Bake at 450 degrees for 10-15 minutes or until golden brown.