Perhaps this man was not a gun maker, but a merchant that sold other's guns.
His name is interesting. The Jean would indicate a French speaking Belgian origin and the Van would indicate a Flemish speaking area.
Determining the origin of a gun is sometimes fraught with frustration, but can be great fun as well.
This is a name that is new to me and I hope all is soon revealed.:}
Best,
John

Humble member of the League of Extraodinary Gentlemen (LEG). Joined 14 March, 2006. Member #1.