Show HN: I Built the World's Largest Cap Gun [video]

About a month ago, I found a toy cap gun at my parents house. Remembering how fun they were, I decided to make the World’s Largest Cap Gun. The video shows how I built it and showing it off to David Dobrik and his friends (it almost didn’t work; the video covers that too), but I wanted to highlight a few other interesting things.

- I didn’t know David Dobrik before this video and was thinking about how to contact him. I decided to make a TikTok explaining that I was building this ridiculous thing and thought he’d enjoy playing with it. It got over 4 million views and he commented on it and DMd me to figure out the details. You can view that TikTok here: https://www.tiktok.com/@nick_ohara/video/6985282649858329861

- The biggest problem I had was trying to create the explosives. I use Armstrong’s Mixture which is a combination of potassium chlorate (found in matches) and red phosphorus (found in the striker on match boxes; my research showed you need to scrape it off). It’s pretty difficult to get raw red phosphorus, so I tried another oxidizer, sulfur. It didn’t work and I didn’t have time to scrape a bunch of match boxes. After my TikTok went viral, I only had 1 week to finish the build and ship it to him, so I was super stressed. What ended up working best was crushing up match heads then CUTTING off the striker, taping them together, and smashing it with a hammer. Realizing I could cut the striker off instead of scraping it absolutely saved me.

- I originally used springs to power the hammer to cock it back but found they weren’t reliable enough. The springs would stretch too far and would get to a point where they wouldn’t spring back. So I used latex tubing which was much more dependable.

- Shipping this beast was super expensive. I had a custom crate built by some friends who made it for free. Two day shipping was $9,000 and 5 day shipping was $1,500. I obviously opted for the 5 day shipping.

- Once we arrived in LA on Sunday night, we tested some of the explosives with a hammer. The gun was shipped to David’s house directly, so we didn’t have the luxury of testing the whole gun beforehand. I ALWAYS wear safety glasses but forgot this one time. And this one time, the explosion had some shrapnel and it got into my eye. I went to the eye doctor immediately and they cleaned it out. I was very lucky it wasn’t anything major and also that we were filming on Tuesday, so I had a day to recover.

- I highlight a lot of things that went wrong at David’s in the video. But even with all those things going poorly, David was super accommodating, understanding, and patient with us despite being stressed with other bits he was recording and editing.

- Lastly, this project was super expensive. Somewhere around $8-9k. The actual cap gun was around $2,500 (parts, tools, paint, etc), shipping was $1,500, traveling was $3,500 (Airbnb, flights for me and my two friends who filmed, rental car), and then other expenses for filming gear, food, etc.