This'll be a full WIP from start to (mostly) finish. I'm withholding one section as it'll be its own tutorial.
After cutting the end off his normal weapon, I need to create the skeleton for his new one. To scale it, I line his hands and hilt over my tablet and zoom out until the shapes roughly match. (See how slick that works?)
I then use a piece of thin, clear plastic from a Privateer Press container and trace the weapon out at the correct size.
This, I cut out.