Faction Weapons would be Exotic weapons that are only sold in towns initially of a certain faction.
(Ex: Player in Spain captures a British Town, town still sells British Faction Weapon)
They could also be unlocked in a Blacksmith by doing a quest to get the 'Parts' of the gun, requiring the Player to get them by destroying ships of that weapon's faction.

Weapon Idea List:

Britain - Belton Flintlock

A rifle that holds 8 rounds.
It would have no bayonet, 14 second reload, and damage falloff slightly better than the Flintlock Pistol. 90% Accuracy. Damage on body shot similar to Pepperbox, damage on headshot identical to Musket.

France - Musketoon
A rifle that holds 1 rounds and a Bayonet. 4 Second reload, with damage identical to the Musket (excluding body shots which would have greatly decreased damage, and the bayonet that would have the damage nerfed to about the knife's damage.)
100% Accuracy.

Spain - Miquelet Pistol
A pistol with 1 round. It would have 3.5 second reload with damage and accuracy identical to the Flintlock Pistol. It would have less falloff and more accuracy.

Pirates - Heavy Axe
A melee weapon with a 6m range and very high damage. It would have incredibly low attack speed and parry speed. (Basically just the Axe of that one melee crew member)

Anyways thanks for reading my rambling :>