Here is what I know. It is a flintlock with a set trigger. I believe it is an 8 bore rifle. the barrel is rifled so its not a punt gun. it also looks like its a solid steel barrel (as compared to a "Damascus barrel") It doesn't look like a swamped barrel but it is slightly tapered.
So I was told that my grandfather called it an "Australian Buffalo gun" but not sure if that truth or just an tall tale.
Over all the rifle is in bad shape and it doesn't look like it was a top quality piece to begin with.
my brother was saying I should get the gun appraised before I try to restore it because it would be a shame if my cleaning effort ruined the patina (he watches too much Antiques Roadshow) but I think most of the screws holding the lock to the stock are not original and the front site is not original as well.
So with out further ado, the pictures

The photo doesn't do the gun justice. It is a big rifle. About 53.5 inches long with the barrel at about 37 inches.

The bore is about 13/16 which is 8 gauge.

Those are the only markings on the gun

Close up of the action. There may be some writing there but it is all but faded out.

The other side of the action