How do I kill One-Eyed Jack?

Hint 1 of 5:

If you've read some of the literature, you'll know that only one weapon will
kill someone as powerful as Jack.

Hint 2 of 5:

You need Captain Nichol's sword.  See the previous question for more help.

Hint 3 of 5:

Just keep swinging at Jack.

Hint 4 of 5:

He'll be gone forever after you've "killed" him twice.