Since its a government done "Belgian" conversion, there is virtually no chance it saw any service before the CW... because the conversion program was almost exclusively confined to unissued arms. In fact, as there is no classification stamp on the off side, it was unissued when converted. I'd bet a dollar it did see a lot of service in 1861-1862 and probably later.
Arms were divided into 3 groups. Class 1 as made after 1822 and unissued, Class 3 was made before 1822 and issued for service. All Class 1 guns were converted, All Class 3 guns were condemned and sold. Class 2 guns were those that fell in between, either in new condition but made before 1822 or made after 1822 and having seen some service but in otherwise excellent condition. These were not originally intended to be converted but some were, especially in 1860 when the demand for arms outran the available supply. Only Class 2 and 3 arms were marked. It wasn't considered necessary to mark Class 1 arms as most were still in their original packing cases.
Arms were divided into 3 groups. Class 1 as made after 1822 and unissued, Class 3 was made before 1822 and issued for service. All Class 1 guns were converted, All Class 3 guns were condemned and sold. Class 2 guns were those that fell in between, either in new condition but made before 1822 or made after 1822 and having seen some service but in otherwise excellent condition. These were not originally intended to be converted but some were, especially in 1860 when the demand for arms outran the available supply. Only Class 2 and 3 arms were marked. It wasn't considered necessary to mark Class 1 arms as most were still in their original packing cases.