Thanks for the replies, but my question should have been, "What are these cars hauling to or from Sherman, TX?". When I saw them, they were on an overpass above a 4-lane highway and stretched out of sight in both directions.
That's a lot of something that's very dense. These cars don't have enough cubic capacity to be hauling 100+ tons of grain or cement. Foundry sand? Maybe, but that's an awful lot of foundry sand. I'm not aware of any source of sand in the Sherman area and I'm pretty sure there is no foundry there that would use that much sand. Fracking sand? Again, maybe, but I'm not aware of that much sand being shipped from Sherman and I'd certainly have heard of any gas drilling boom in that area (I live only 30 miles south of Sherman).
Since these AOKX cars all looked to be in uniformly excellent condition with no graffiti, etc., there is also the possibility that they are new (I wasn't close enough to see a BLT date) and waiting for their first assignment. If that;s the case, I'd like to know who built them and exactly where.