I always thought #5 chilled shot would be the berries, but all I can ever find is #6. It works very well but takes a bit more picking to clear the meat of tooth-crackers.
My Bess was a carbine caliber (16 ga/0.662" bore). Your Bess I'm assuming is an 11 ga. A good, mild 12 ga load would be 82 gr. FFg (3 drams) and about 1-1/8 to 1-1/4 oz shot. You could start there and maybe head up to around 90 gr. and 1-3/8 oz. shot. By happy coincedence, your powder measure throws about the right amount of shot at a given powder volume. A little more shot and less powder (opposite of what you might think) gives you a tighter pattern and stretches your range. No matter what, you probably won't be patterning reliably past 35 yards, but that's plenty. Shoot at some paper and see how she patterns.