Start by removing the skins and seeds from the scuppernong or muscadine grapes. Peel the sand pears and chop them into small pieces.
In a large, heavy-bottomed pot, combine the grapes, chopped sand pears, lemon juice, and the packet of pectin. Stir well to ensure that the pectin is evenly distributed.
Place the pot on the stove over medium heat and bring the mixture to a gentle boil. Stir occasionally to prevent sticking.
Gradually stir in the 4 cups of sugar, allowing it to dissolve completely.
Increase the heat to high and bring the mixture to a rolling boil. A rolling boil is one where the boil continues even when stirred. Let it boil vigorously for about 1 minute, making sure to stir constantly.
To check if the preserves are ready, place a small spoonful of the hot preserve mixture on a cold plate and let it cool for a moment. If it sets and wrinkles when you push it with your finger, it's ready. If not, continue boiling for another minute and test again.
While the preserves are still hot, ladle them into sterilized canning jars, leaving a little headspace at the top. Wipe the rims of the jars to ensure a proper seal.
Place sterilized lids and rings on the jars and tighten them securely. Immerse the sealed jars in a boiling water bath for 10 minutes.