You used the terms "arsenal model" to describe the piece; is the vent drilled to scale, and too small to accommodate a fuze?
The vent looks like a pinprick since it is to scale in diameter; it is not drilled through though I don't think; there would be no need for that although it would make it just a touch more realistic. I have here and have seen full models, where everything is modeled exactly to scale, or so it appeared. Then I've seen models which empahsized the carriage and simplified the barrel which was just there to complete the general appearance, and vice-versa.
One of the finest models I have, in very large scale too, is of a 12-inch seacoast mortar, US, and it is a carriage model. The carriage is executed in unbelievable detail, all same materials as large one, etc., but the barrel is WOOD. This model was made at Watertown Arsenal MA, and is listed in their annual report for 1896 or so.