I agree that there is some merit in Doc’s suggestion, although I am not totally convinced. Post 1928 tracers were headstamped “G.I” so would a round headstamped “G1930 VII” be confused with a tracer? I would have thought there might have been more confusion during WWI when there were ball rounds marked “G17 VII” and tracers marked “VIIG”, complicated by Governement Cartridge factories using “G17F3” for example.
Also, I would like to know why the headstamp was changed from “GB” to just “G” around 1907? I have wondered if it was to standardise on single letter codes like K, B, G, but then where does KN fit in?
As an aside, I don’t think GB ever made any tracer ammunition. Does anyone have an example?