Nominally, the standard 16 bore is .662". A pure lead ball that size, weighs 1 ounce, or 1/16th of a pound. 7000 divided by 16 = 437.5 gr.
20 bore is .615 (not .620") and a pure lead ball that size is 1/10th of a pound. 7000 divided by 20 = 350gr.
Of course to load into the bore and be "clean shooting", one needs a smaller ball and lubricated patch making a snug combination.
Some fellows do well with loose combinations of ball and patch while others do well with bare balls and wads of some other materials.
In the post about RB accuracy from smoothbores, of the picture with 4 targets, the far right target 3/8" or so (4 shots only) than the others, no
patch was used around the .595" ball, but just a wad below the ball and one over, ie: "bare ball".