I love grappling hooks. Every action figure had one when I was growing up, but few real ones exist in our world. After creating a "real" throwing grappling hook I couldn't resist building a plausible grapple gun. I had several mandatories for this build:
• All-metal, if possible.
• Self-retracting hook and line
• Look "practical" as if it could function
• Built 90% from found items.

Here's the result. It's built almost entirely from found items. I wanted something that didn't look like a conventional gun. I also wanted something that would look like you could hold onto the grip and be pulled upward. Installed in the body is a retracting line that keeps the hook snug in the barrel of the gun, but you can pull the hook out a couple feet, and it retracts back perfectly. It doesn't shoot .... maybe next build.