Just a note. I looked at these and they are not the same gun; you can see the serial # on the trigger bow of the first one, and the CC's are pretty much gon.
I think it is funny that everyone selling one thinks they have a prize from an auto race in 1906. The term Grand Prix has been so connected to Formula 1 that people think it means the race. The translation general comes out something like "Formula One Grand Prize of Monaco" etc but the term Gran Prix is generally not translated. The gun I bought is dated to 1929 or so. Little late to finish the prize and award it.
The gun ws not awarded as a prize, but was awarded a prize for industrial design at the Milan Exposition. They apparently labelled this model like that for as long as they made it after the exposition.
Also noted in a catalog from that period that the gun was only available "double full choked", which is consistent with the barrels and not the proof marks.