It’s a French made shotgun by JB Ronge and Sons in Liege, France.
Those H.J.A.B. are likely maker’s initials.
Is it a 16 gauge?
Many of those shotguns were made with "specialty" marks, such as HJAB Special, which more likely indicates the initials of a US business that bought and sold such guns as promotional items for their stores or whatever.
I knew a fellow that was given a similar shotgun when he bought a bunch of barbed wire, from the "Bellknap Hardware" company, while he lived in the southern US.
OP, your particular shotgun is very nice, most of them weren't that well done.
You will need to be careful about the loads you shoot through her though and it might even be chambered for shorter shot shells, that may not be available today.
The engraving is nice and done in a common style for those shotguns back in the day.
The steel used for those receivers is on the soft side, so again, use caution and make sure you know the chamber dimensions.
It wasn't uncommon for many folks that owned those guns to have the forcing cones opened up so they could use readily available, off the shelf ammo.
