Even "back in the day", Gastinne Renette sold guns they didn't make, or had made for them in France. Not at all unusual to see Belgian proofs on a GR-marked gun. But with the Bernard barrels and Paris proofs, this one goes back far enough that it's much more likely that GR played a hand in building it as well as selling it.

I had one GR-marked OU--very nice gun--based on the Petrik design. That's the original design of the OU's with a sliding breech hood which Remington used for the Model 32; Krieghoff since then. The difference with the Petrik OU's is that they were often quite light and designed as field rather than target guns. There's a 16ga on the Safari Outfitters website currently. 28" barrels, weighs less than 5 1/2#.