I am interested in the comments made about the hardening of rivets. I'm no engineer!! When I restored my 2 pounder field gun I had to remove a few rivets from the shield. These were small dome head and countersunk. I could not drill them with even the highest quality drill bits. I could not grind the heads off as they are countersunk. The only way I could remove them was to cut the dome off and heat them with an acetylene torch till they were red hot and drive them out with a slim drift. Does this mean they were of a different steel that hardens when hot.
Ron