The Hand Cannon was an early firearm, possibly one of the oldest in existence. It was the Special Weapon of Vlad the Impaler.
The hand cannon was simply a barrel with some kind of handle, although there were many variations. Most drawings depict it with a wooden stake supporting the barrel, with a wooden stock in the back. It had no trigger; the powder was lit through a touch hole on top of the barrel by means of a smoldering piece of wood or coal, or slow-burning matches.
The version shown in the show appeared to be little more than a barrel mounted on the front of a thick plank, with a handle on the bottom that doubled as a war spike.
The Hand Cannon was based on the Siege Cannon (wich Vlad also used), but until the Hand Cannon was invented no one could develop a way to shrink the cannon's size while also making loading the weapon and producing musket balls possible.
The hand cannon was possibly the oldest portable firearm to be used in battle. Although inaccurate and slow to reload, it was more powerful than any other weapon of its time, piercing even plate armor. It also had a spike on if so it could be used in melee combat (being roughly the medieval equivalent of a bayonet). In Europe, it was used until the 1520's, when more advanced matchlock Arquebus firearms replaced it.
After the fall of the Mongolian Empire, the hand cannon evolved into the 3-Barrel Pole Gun to increase the rate of fire.
It was tested against the Huo Chien. It was given the edge due to the fact it could actually kill and had melee capabilities, while the flaming arrow proved to be highly ineffective.