I wrote a short article about this over at 80 Level, check it out here:
Made as a free time project, the WildFyre Blunderbuss is a highly powered very inaccurate and short-range shotgun-type weapon. Made from scrap materials, it opens up at the back (the shoulder rest is attached to a hatch) where you can insert garbage. Inside it is grinded into smaller shrapnel, which is then blasted out through the front by igniting the higly flammable ‘wildfyre’, held in the transparent containers at the side. On the other side there’s another container containing oxigynated air to drive the wildfyre through the system and help it ignite with extra force.