Very interesting. A 20 Lb. propane tank and angle iron is used to make a spigot mortar round. It is about using what you have at hand when you need something. Don’t have a howitzer round? No problem. Be inventive and adapt to the situation. For what it is worth the same round could be fired out of an air cannon as well. With the propane tank warhead it could have any type of charge in it; Chemical, HE, shaped charge, Low order explosives or incendiary. Kids, don’t try this at home….