This is a rescale to 4mm:1ft of the the 3mm:1ft model I have uploaded before.
The prototype is a private owner end-tipping rivetted steel-bodied coal wagon of 16t capacity, similar to the early British Railwys 16t designs but with a thin vertical stanchion in the side panels. The interior bracing walls on this model are to preserve straight sides through the printing and finishing process and can be removed when you receive the model. Carefully scrape up the ends of them where they join the inside of the sides with a sharp scalpel point, over and over again, until a little bit of flexing causes them to split out (note: this might be more difficult with the white versatile plastic, which is less brittle but tougher). If the sides distort after a time, you may be able to soften the plastic in hot water put something the correct width inside to make them straight again, and stop it bowing inwards while it cools. Of course if you're going to model the wagon loaded (and hide all my nice internal rivets and interior door detail) then you can just leave the bracing in there.
Many thanks to tigger 1805 who requested this rescaled design, for sending his photos of the unpainted but basically finished first ever print of this model.
See on RMWeb (21D)
https://www.rmweb.co.uk/topic/182811-3d-printed-bodies-of-early-all-steel-mineral-wagons/#comment-5344253