A simple model based on an early type of Chinese 10th–12th-century gunpowder weapon or a flame thrower called the "Huo Qiang" or "fire spear/lance". These sorts of gunpowder-using "firearms" (in the literary sense) were among the very first gunpowder-based weaponry ever. Their workings were really simple, a bamboo tube to hold black gunpowder granules at the end of a spear/lance and a slow match in the base of the tube, When ignited the burning gunpowder was to spew out flames and sparks at any foe of yours who you wished to burn up. These sorts of weapons are the ancestor of modern firearms and flamethrowers.
Later it was figured out that you could add projectiles of sorts into these gunpowder-filled tubes which then made them not just spew out flames but projectiles too. This then gave birth to the first actual guns/firearms.
This model was based on the depiction of such a weapon in the Huolongjing, a 14th-century Ming dynasty treatise on firearms and fire-based weaponry.
Sorry for the bit of a Hiatus, had some goings.
This model and renders were commissioned by wild arms research and development to be used in their new book titled "Flame assault shoulder weaponry m202A1 flash"