It isn't a field gun carriage. It does have a French model elevating screw and plate, but the plate is too thick to be a Gribeauval model. I seriously doubt that it is a Gribeauval siege gun carriage also. There is a place on the breech for a sight. It appears to me to be too narrow a gun carriage to be a Gribeauval model. And it is unlike any of the artillery models in the Invalides. I was there this past summer and photographed the models.
It might be an Austrian gun tube, but I'd have to research that just a bit more. It should be noted that three nations' artillery arms used double trunnion plates: the Austrians, French, and British. The French used them for the 8- and 12-pounders, the Austrians and British for 12-pounders alone. The British used double trunnion plates for the 12-pounder with a bracket gun carriage.