Well why not try a Belgian .75 Caliber Percussion Wall Gun? Ian from Forgotten Weapons checks out one very massive Belgian .75 Caliber Percussion Wall Gun.
If you like big guns and black powder, this video is certainly of epic proportions.
This Belgian .75 Caliber Percussion Wall Gun is one very large example of a wall gun. As Ian from Forgotten Weapons explains, wall guns usually were used to protect fortifications. This example in .75 caliber has quite a unique way to load it from the breech end. That beats loading from the muzzle end of a weapon this long.