One joule is roughly the amount of energy needed to lift an apple about one meter against Earth's gravity.
For the uninitiated, a railgun "uses current to generate extreme magnetic fields that propel a conductive projectile to high speeds," explains Zee's YouTube post. Zee's railgun weighs 250 pounds and has 56 480-joule capacitors that make up the power supply.
Ziggy Zee perfected the shooting capacity of his high-velocity DIY weapon by testing its firing potential many times in a field. In the first launch, he admits that "connections needed to be secured better against the extreme magnetic forces." After several attempts, the YouTube clip shows the railgun pulverizing an object from afar. Railguns are commonly developed and used by the US navy. A redditer also 3D printed one for pleasure more recently.