Shipping titanium dioxide - Model Railroader Magazine

For my paper mill project, I am thinking about adding titanium dioxide to the incoming loads for page whitening. What I am wondering is how its shipped. I do see dupont tank cars, but I dont know if they are shipped via covered hopper. 

As a theory, I was wondering the weight per volume of tio2 so it can be shipped dry via covered hopper hopper. It came out to 4 grams per cubic cm.

Now, converting a cubic foot to cubic cm, it comes out to 28316 cubic cm per cubic foot; 28316 cubic cm * 4 grams per cubic cm = 113264 grams; 113264 grams = 249.7 pounds.

taking the full capacity of a acf 2970 hopper with a maximum load of 100 tons my load will be the folowing; 249.7 lbs per cubic foot * 2970 cubic feet = 739530 lbs; 739530/2000 = 369.8 tons. 269 tons over maximum

lets compare this to a cement load which is roughly 94 pounds per square foot. 94 pounds per cubic foot * 2970 cubic feet = 279180 pounds; 279180/2000 = 139.6 tons 40 tons over.

Is it common for railroads to ship containers that are 1/3 full at max weight capacity?