Learned the hard way that the plug is the part that actually matters here. I used to grab whatever threaded cap fit and call it good, but after seeing enough of these blow apart I only trust PVC fittings stamped with a pressure rating like NSF-PW or SCH 40 with a PSI number on it. Drain caps and test plugs are made for water sitting still, not for a boom going off inside a pipe, so the threads strip or the whole cap rockets off like yours did. There is no single chart for potato cannons since they aren't a real product, but you can look up the pressure rating tables from the pipe maker and match the cap to the pipe's rating. Grab a threaded cap made for pressure, not a cleanout plug, and if you can't find the PSI stamp on it, leave it on the shelf.

My buddy did the same thing but with his alcohol stove and a little digital scale from Walmart that cost like 10 bucks, and he figured out he was carrying almost a full pound of fuel he never touched on weekend trips. The funny part is he also learned he was boiling like twice the water his meals needed, so he started cutting that back too and shaved even more weight. He said the scale paid for itself in one season just from not buying fuel he didnt burn. Weighing your bottle before and after a trip is a genius way to see what you actually use, I do that at home now just to track it. You got me wanting to dig out my kitchen scale before my next trip.