I figure the Musket, Flintlock Pistol and Clockwork gun are all smoothbore
pepperbox style guns, with three barrels. Flintlock Rifle, as has been mentioned is a rifled single shot long gun, also known as a
Long Rifle. In game it might not be that exact type, the one in my head is specific to the North American frontier in the late 1700s and the minie ball ammo used is US civil war era, 1850s. I wouldn't want my precision weapon to be a pepperbox, too many parts, too many places for it to break
But given that it's basically an pirate design, basically simplifying the concepts behind the guns they salvage to the point where they can build a sniper weapon and ammo with the most basic workshop, I see no problems with it, if you're unlucky enough to not get any sniper guns by the point where you can build one, it's going to be useful, if you run out of ammo for your looted sniper rifle, then it can be useful, it can potentially do really good damage for when you get it.