It is silicon bronze (6% silicon, 94% copper less impurities) and casts very well (great for sculpture, very fluid when melted) but not the strongest possible alloy. But for a half scale tube, it should be strong enough assuming the operator stays away from anti-aircraft duty. It has a 1" diameter chamber.
As I recall, it was $2.20 a pound and the raw casting plus gates and sprue weighed about 95 pounds. I actually cast four of them, the first three in petrobond sand and the last as an investment casting. The finished weight is only 28 pounds so a lot of it becomes chips, but they can be remelted so they aren't totally waste.
The advantage of casting is less waste and integral trunnions but the process is expensive or time consuming (make pattern, make mould, melt bronze, set up foundry for casting, pour bronze, clean up, yada yada yada.) But a bronze version of a bronze gun really looks nice.