Combine the berries and water in a large pot over medium-high heat and bring to a boil. Lightly smash the berries with a potato masher or large spoon.

Maintaining a steady boil, cook berries for 20 minutes.

Place a large bowl beneath a fine-mesh strainer (or a regular strainer lined with several layers of cheesecloth). Save the juice and discard the berry remnants and seeds.

Measure sugar In a medium-size bowl. Set aside.

Measure the blackberry juice. You should have close to 3 ¾ cup. If you are a bit short add water to measure 3 ¾ cups. If you have more than 3 ¾ cup, save the extra juice for another use.

Combine juice and pectin in a 6 to 8 quart sauce pot Stir well to combine.

Add the butter and bring the mixture to FULL ROLLING BOIL (a boil that does not stop bubbling when stirred) on high heat, stirring frequently.

Add the sugar and stir well.

Return to a rolling boil and boil exactly one minute, stirring constantly. Remove from heat and skim off any foam.

Quickly ladle into the prepared jars to within ⅛ inch of top. Wipe jar rims and threads with damp cloth. Cover with lids lids. Allow the jelly to sit at room temperature for 24 hours then refrigerate (for 3-4 weeks) or freeze (for 4-5 months).