Jack (weapon)

Jack is a more powerful version of the Ripper.

Location
Jack can be found inside the Deathclaw Sanctuary on an Enclave Officer corpse. Refer to the map for directions. You'll find the officer in the shadows next to a puddle of blood and a giant ant corpse. Note that this weapon is not obtainable until after the Enclave shows up in the storyline, though if you clear out the Deathclaw Sanctuary early, you can always go back later.

Trivia

 * This weapon is a nod to Jack the Ripper, one of the most infamous serial killers in history.