Colorado
The ACF 2 bay 70 to covered hopper and the PRR H-30 date back to the 1930s. As HW said they were used for heavy commodities like cement and sand.
Take a look at the Atlas product announcements for some basic info.
http://www.atlaso.com/o70tonhoppers.htm
http://www.atlastrainman.com/F...tmo3bayps2hopper.htm
In the 50s the higher volume 70 ton covered hoppers (like the Atlas Trainman PS-2) began to be used in grain service. But they were by no means in the majority, 40 foot box cars remained the norm for grain service until larger 100 ton covered hoppers revolutionized grain transportation in the 60s.
Here is a 1958 photo showing a truck, box car and a PS-2 70 ton covered hopper all being loaded with bulk blended feed. From the Tacoma Public Library collection.
The 1950s were a fun time when you could see loader equipped box cars, covered hoppers and wooden sheathed box cars in the same train pulled by either a GP9 or a ten wheeler.
Here is a Ron Nixon photo of a NP S-4 with covered hoppers likely in cement service in Spokane in 1953.
HW
I've never seen a B&O wagon top hopper. Pictures please!
