These warriors are experienced in the use of European firearms.
A musket is a status symbol among the tribes, even though it is not as useful in a fight as an old-fashioned and reliable bow. It is, however, a mark of personal bravery that a warrior has taken one in battle, or been considered worthy enough to have been given one of the precious weapons. These men are the most irregular of forces, unwilling to take formal army discipline, yet willing to fight like men possessed when the need arises.
In the early days of European settlement, the Native Americans were happy to work with the various foreign powers that colonized America, even forming alliances against their neighbours and other Europeans. The tribes soon became involved in trade, fought wars because of the allegiances they forged, and were forced into new alliances as old tribal enemies took up with Europeans.
Short of the units available with The Warpath Campaign DLC, Mounted Tribal Gunners are the only missile cavalry available to the Native American factions in Empire: Total War. They are similar to Mounted Tribal Auxiliary: cheap and fast firepower, but not as organized or numerous as Light Dragoons.