Preheat oven to 425F. In a large bowl, sift together flour, salt, soda, and powder. Using a pastry blender or two knives, cut the shortening into the flour mixture until coarse crumbs form.
Add the buttermilk, tossing with a fork until a dough forms.
Turn the dough onto a lightly floured surface. Gather into a disk. Knead lightly a few times until smooth. (The dough may be made up to two hours ahead, wrapped in plastic wrap, and refrigerated until ready to use.)
Pat the dough to 3/4 inch thick. Using a biscuit cutter or a glass dipped in flour, cut out the biscuits. Place them, two inches apart, onto an ungreased baking sheet. Gather dough trimmings, pat to 3/4 inch thick, and cut out more biscuits.
Bake until golden brown, about 12-15 minutes. Serve hot.