Hi Steve,

The most comprehensive reference article about the CR bogie wagons is by Jim MacIntosh in TTL No. 68. Essentially the first wagon 72000 to Diagram 50 was rated at 50 tons, but I think that would be its iron ore capacity, so probably 30 tons with coal. Subsequent batches of the steel bodied varieties to Diagram 54 were rated at 30 tons. 

In that article is a photo of 72000 as built, (NRM ref SRX456) and I took the lettering of the wagon from that. It is however a works as built photo, so it may be that somewhere there is a photo of the wagon in later years with different lettering and showing a different capacity. ( If so, please tell me  ! ) The photo on p99 of "Caledonian Railway Wagons" by Mike  Williams shows the Diagram 50 and a Diagram 54 together, so it must be 1905-1910  ish. The Diagram 50 still has the lettering on the top plank of the body and the smaller CR. 

All the lettering on mine came from the HMRS pre grouping wagon methfix transfer sheet. 

Hope that helps. 

( I do like answering questions like this since every time I go back to reference material I invariably find all sorts of other interesting stuff )