How big is it? About 75mm?
It doesn't look quite big enough to be a 75mm...maybe a 40? Potential old Bofors round?
I'm guessing the "40" is the year of manufacture and according to wiki there weren't many of them around in 1940 and mostly in France.
But looking at other 47mm stuff there is this:
http://en.wikipedia.org/wiki/Cannone_da_47/32_M35
Used by the Romanian army too.
I dunno. Where's LD. He would know.