SpudFiles

I use a lubricant called "Super lube" on my piston, its a synthetic lubricant and contains PTFE. Comes mostly as a light grease.

On the face where the piston meets the edge of the pipe I use silicone grease as it makes a nice seal.

Good news! I just finished my THIRD attempt at a piston cannon, and it worked! Its loud as hell... I used white lithium grease, not the spray kind, it came in a tube.