Ok...so this might look steampunk...and it sort of is...but all features are in fact from real flintlock weapons developed before 1800.
The revolving breech, with a feed from both powder and ball magazines in the butt was a real invention, seen in Italian Rifle of 1690 by Michele Lorenzoni. These magazines hold 5 shots, to reload the butt plate is unclipped and rotated clockwise, pivoting at the top, the magazines are then reloaded from the rear.
(Advantage: reloading more quickly and whilst prone.)
The covered flintlock mechanism was used on a French sporting gun of 1760.
(Advantage: Dry powder, prevents smoke and flash from pan escaping)
The brass sighting tube has been covered before.
Use: Long range sniping of multiple targets.