The famous "King howitzers" of the late 18th C. came in two sizes, weighing about 32 and 60 pounds respectively. Both models were bronze. I've never heard of any made of iron, but anything is possible I guess. Is this a real variant, or is it a transcription error?

While you are looking, think about the efficiency, or lack thereof, of having so many different types of artillery at a single outpost.