Thanks Mike, that's exactly the sort of information that I was hoping for. There was a lot of that I didn't know and I imagine that applies to most onlookers.
You've got to love this forum.
Dave
ps I remember seeing (and have a photo of) a turkish skull on display in a little museum in Krithia on the Gallipoli Peninsular with one of these balls lodged half way through right on top. The 'tin hat' was introduced to prevent or reduce such casualties and most certainly did so.