Prototype information for the modeler

I model BNSF, but I think this could work for about any other RR.  I have several different covered hoppers for grain service.  I have a question. 

Is the grain moved to larger cars that have more capacity and moved to its destination or is it loaded at the point of origin and remains in that car until it reaches its destination?

  Once in the car they go to where ever they are being shipped.I have never personally seen a car unloaded into a larger car.

Will,

  Grain is shipped in covered hoppers that have a capacity in the 100-112 ton range.  Those smaller 2 bay covered hoppers are used for thing like cement.  Once a covered hopper is loaded, it is routed to the export elevator for ocean shipping or a grain miller for processing.  At one time(back in 40' box car days), there was a 'mill in transit' billing that gave the shipper a deal if the grain was routed to a specific flour mill and the flour was then shipped out over the joint railroads that published the rate.  I m unaware of the being used anymore as most grain is shipped in large blocks of cars to major processing facilities.

Jim

Jim,

I remember hearing about the mill in tranisit.  I thought it involved covered hoppers, but it makes since with the boxcars.  That is where I was probably confused.