BN 533643 and 533765 are aluminum rotary dump coal gondolas. Both were built by BSC in 1990-1991 and are built to hold 4400 cubic feet of material. These cars are classified as gondolas and not as hoppers because there is no discharge gate on the bottom. The coal is loaded into the top, and it is also removed through the top. Each car is fitted with a rotary coupler on one end (the end with the rotary is designated by being painted), which allows the car to be completely tipped over while still being connected to the rest of the train.
BN, and now BNSF, loads huge amounts of coal from the Powder River Basin into full trains via flood loaders. The train slowly creeps through the loader and each car is filled to capacity within a few seconds. When the destination is reached, the train is unloaded without uncoupling anything. Each car passes through the rotary dump, which grabs the car and flips it over, quickly dumping everything, then righted again and on to the next car. In the middle of every train is a double-ended rotary car, which makes it so both front-end and DPU locomotives are coupled to a rotary coupler. Without a rotary coupler next to a locomotive, the locomotive would be tipped over when the car reached the rotary dump.
BN 533643 and 533765 represent two of many ex-BN cars found on BNSF today. They have not been patched or painted. They are older than much of BNSF's fleet, and therefore have weathered quite heavily. Many also have replacement ribs on either side. When empty, you can see that they have two ribs, whereas other coal gondola's have 3 or sometimes 5.
These cars feature the distinctive "bathtub ring" on the interior of the car. A few years ago BNSF began spraying a glue-like material over the coal loads in order to keep the coal dust down. In some areas the coal dust was so bad that it had gathered in the ballast, making weak areas that led to derailments. The new spray causes the dust to stick to the inside of the gondola above the mound of coal, leaving a dark "ring". This ring will not be visible on other roads such as UP because they do not spray their loads.
The models are both Athearn cars, lightly modified and heavily weathered.