Wow, Geeky stuff alright.
Perhaps leading to the proverbial mad scientist if you people were not psychologically stable.
I made a few nitrate bombs and rockets. Also a small cannon. The ball bearing went through two one inch planks, three fences and an old garage door coming to rest leaving a very light mark on the car inside the garage.
Close one.

Good ones, Brent, Steffan, Peter.

I also wanted to make a Tesla coil. I settled for a miniature which gave me some 2 cm sparks from a 3 volt supply. I was 13/14 at the time.
Where's jjj? I'm sure jjj may have some stories. I assume that jjj started later.
Don't confine this thread to the kid stuff we did. Its the later achievements that are all interesting as well. Like what photo remains the most rewarding personally. That kind of stuff. Or, perhaps you may have been hoping for a Nobel Prize nomination. LOL
I did not have much time to read these this morning but here I still am. Have to go in a rush now. Its riveting. The stories that is.
Cheers