Hello tal38
Welcome on your first posting
Nice firearm

You will need to remove the forearm, and take the barrels
away from the action.

On the underside of the barrels will be proof marks

Belgium marks are like this

https://www.shotguns.se/html/belgium.html

Please post pictures of the proof marks

Again, Welcome
Mike


USAF RET 1971-95 [Linked Image from jpgbox.com]