It is a long story .
.69 " was " 18 balles à la livre de France " 18 balls per french pound ( 489 grams )
as comparaison , the actual 20 ga/.62 ' ( 20 balls to the english pound / 453,5 grams ) was 28 balls to the french pound .
The history of gun making in the city of Liège ( Luik in flemish ) is a long one . So.... in the early years of the american civil war
the various Belgian factories sold weapons to the Confederates and bought them back years later when muzzleloaders became obsolete .
Said muzzleloaders were rebuilt in various configurations to be sold in Africa and South America . Some of those composite were ... well ... " interesting " . As old part became scarce , some substitutes were made . Some barrels were high pressure seamless tubes .
Later in time , Americans started the black powder revival just in time for the last days of the Liège gunsmiths .
Here is a catalog from the "60 on this page , your gun is in it .... or one very similar .
http://www.littlegun.be/arme%20belge/ar ... k%20fr.htm