Gentlemen, what can I say apart from thank you very much. I have now seen the 0.50 round (still live BTW) it has
SL 43 stamped on the base. I wonder were it was made? I don't really want to kick this thread off again but all this is really interesting stuff. My old friend will donate the round to the small RAF Metheringham Museum located on what's left of the old RAF Metheringham airfield near Metheringham, Lincoln. My son (an RAF Regt Reserve NCO) will ensure the round is made safe. Here's the link to the ME 473, the 207 Sqn aircraft. Click on search and then type in ME 473, then click on find.
http://www.207squadron.rafinfo.org.uk/