Crush 1 cup of the berries in an 8-quart Dutch oven or pot. Continue adding berries and crushing until you have 5 cups crushed berries. Stir in pectin. Bring mixture to a full rolling boil over high heat, stirring constantly. Add sugar and lemon juice. Return to a full rolling boil; boil for 1 minute, stirring constantly. Remove from heat. Quickly skim off foam with a metal spoon.
Ladle jam at once into hot sterilized half-pint canning jars, leaving 1/4-inch headspace. Wipe jar rims; adjust lids. Process jars in a boiling-water canner for 5 minutes (start timing when the water returns to boil) adjusting for altitude. Remove jars; cool on wire rack