Tiny steel gun powder-box. Gun powder is put in from the top and is released at the bottom when the lever on the side of the main body is pulled. This was used to put powder in the powder-pan (very small bowl) at the end of the barrel next to a tiny hole going inwards to the powder and the bullet. The powder in the pan is lighted by the fuse and subsequently the gun fires.
As the design is quite different from to the silver powder-boxes we are not absolutely sure this is Omani. However it does have the dot in circle design.