I have seen pictures of a wood flour mill that received sawdust and rags in 40' boxcars and shipped wood flour in 40' boxcars this is 1970's and an occasional short 2 bay covered hopper .what would be in the covered hopper?
My guess would be, wood flour, if it's one of the out-bound cars. The perfect car for a dry bulk commodity as wood flour. Maybe the destination ruled what type of car they would receive the flour in, and the hopper was for a specific manufacturer that could handle a 2 bay covered hopper.
In the 40' box cars, was it filled like the grain handling box cars? or in bags.?
Just a thought.
Mike.
My You Tube
Into the 1970's, 40' boxcars were the most common way to ship grain. There were wood pieces that could be put in place to block the door from the inside, leaving a foot or two at the top for grain to be put in the car. Some post-war steel boxcars had a plug-door with a small door towards the top that could be opened to feed the grain in.
The wood flour was blown into the boxcar which had "grain doors"