Not sure when it was used, but it is a really cool idea. If I could wave a magic wand, I would have one that threw 1 oz. In my right barrel and 1 1/4 oz. in my left barrel.
Both cups are the same size, 1¼ oz. 7s for birds and 4s for rabbits? Not sure, definitely cool tho.
I guess I could whittle a plug to throw a lighter charge from one. I don't know how they were used, but It is going back into service.