Well, this morning I mashed and boiled the grapes and set the juice in the jelly bag. Got home and found I had a little less juice than expected. Prepared 9 jars, boiled the juice, added Certo low-sugar pectin (needed 4.5 cups of sugar), boiled it up. I only got 6 jars of grape jelly. They look pretty, though, and it tastes quite good.
I am getting enough raspberries (> 1 lb every 2 days) to make another batch of jam. And I still haven't picked all the grapes (the raccoons are helping with that) so I might be able to get a few more jars of jelly.
I like Bernardin's instructions better than Certo's (Bernardin: never sterilize jars in oven. Certo: sterilize jars in oven; Bernardin: use water-bath canning method. Certo: seal sterlized jars).