This is a video from very amateur madman TheBackyardScientist showing you how to make your own propane rifle. It's pretty simple. So simple you could easily do it in your garage after school with zero adult supervision. Not that I'm encouraging that, because I'm not. As much as I'd love to see you with no eyebrows, I care about your safety. "You do?!" A lot. Okay, a little bit. Not very much. Fine, I cut your car's brake lines during lunch.
Keep going for the video, then ask your mom to wait in the car at Home Depot while you run in for a few things. Tell her you're building a fish tank.
Thanks to Lukas, who isn't afraid of things blowing up in his face because he's convinced that's how he'll get superpowers. Wow, you....keep doing what you're doing I guess.