In a medium saucepan, add blackberries, sugar and ½ cup water to a boil. Stir until sugar is dissolved. Reduce heat to a simmer. Stir occasionally until fruit is soft.
Allow syrup to cool.
Strain mixture through a fine-mesh sieve into a large pitcher.
Add Bombshell Gin and lemon juice to pitcher.
Add ice to fill and stir until chilled.
Add ice to Collins glass and pour mixture.
Top each with ¼ cup club soda.