More information is needed about this piece. There are different alloys of brass and bronze. Is there any history of any of the pieces produced by this company failing? What are the dimensions for this mortar? According to the markings it would appear to have a 1 1/2 inch bore. How were these barrels made? Where they cast solid and bored, or cast around a sand core?
Some time back, Mr. Gatto was either a sponsor or at least was listed as a supplier in the stickies. I corresponded with him about his cannons.
He was clearly using some form of brass (which he called bronze). He posted the ingredients here and there was a high % of zinc in it. The steel liner was cast in place. See pic from his website...
He claimed that he had never heard of one of his cannons/mortars failing after hundreds being sold. After some less than friendly (but valid) critiques of his manufacturing methods, materials and style of his products, he stopped posting.