Gunslinger, welcome to the forum. When you get a minute, stop by the intro thread, say howdy, and tell us about yourself.
In the meantime, I moved your question over to shotguns (support thread is for problems with the site)
We REALLY need pictures, including the proof marks that will be on the underside of the barrel at the breech end, and markings on the frame (you will need to take it apart to see them).
However, Your grandad's shotgun MAY be Belgian- Liege was the gun maker's center in Belgium. Potteau is likely the maker (they had hundreds). Could you please check spelling on the forgeoion? If you find an oval with the letters ELG, that is a Belgian proof mark.