Theoretically simplest firearm that could be built which shoots both ways.

Simple concept for potentially the simplest kind of a firearms that could be built with the lowest amount of resources, tools and workmanship.
What makes this firearm so simples is that it is simply just a metal tube, the kind that you can find from any hard ware store or junk yard, two projectiles with with a appropriate amount of gunpowder in-between that then can be fired with a source of heat placed against the tube heating the gunpowder until it ignites firing both the projectiles in the barrel. this way the barrel doesn't have to have a closed breech to fire thou you will need to be carefully so you don't shoot your self.