The piece looks like about the right size and shape for a British 3-pounder, of which there were many models over the years. It also looks like it is probably bronze to me, as smooth as it is. Even in arid county an iron gun will get rusty eventually. Original bronze Brit pieces are often a dark brown like that one may be. It might weigh 300-320 lbs. or so, gotta look up the wts on them, but again that varied with the model.
The steel mountain gun I fired at the steel plate in a video I linked here recently came out of Afghanistan. The special forces were allowed to take two each from a large cache they found in a junkyard in Kabul. There was also at least one WWI Puteaux tank and some large iron guns that no one wanted to try and ship home. The terrible thing is that all the guns had original steel carriages with them, and when they got to US customs, the agents said the carriages had to be destroyed so it would not be a complete weapon system. Talk about s__t-for-brains! These are antiques fer c---sakes.
