Fireball explosion or just boom? I thought WD40 was changed to CO2 instead of propane propellant recently? It doesnt work in potato guns anymore...
I prefer small 15 gallon garbage bags filled with oxygen/acetelyne welding gasses mixed 50/50.... I shoot them with a tracer from 75 yards. VERY loud. Easily 3 times louder than a tannerite target. No shrapnel either, since it's just explosive gas in a garbage bag.
Even though it's pretty safe, still.... dont do it. Bad idea.