vbkostur
You have received good advice on hopper car types, their period of use and the types of products that they handled. In the early 50s you would have 70 ton two bay covered hoppers like the ACF and PS-2 hauling dense products like sand and cement to locomotive service facilities, glass factories, foundries and cement plants. The 70 ton Air Slide was introduce in 1953 and was used for products including flour and sugar. They would be loaded at mills and would be destined for packaging plants or commercial bakeries. The 70 ton three bay PS-2s as modeled by Atlas in their Trainman line came into use in the late 50s for grain service.
If you are interested in reading more about the covered hoppers available in O scale and how they were used you may want to look at the O Scale Freight Car Guide to 70 ton Covered Hoppers.
https://ogrforum.com/t...-ton-covered-hoppers
And the O Scale Freight Car Guide to 100 ton Covered Hoppers.
https://ogrforum.com/t...-ton-covered-hoppers