Alex,
recently discovered 'Official' information has disproved the old 'metals-saving' theory in favour of 'labour-saving', with only some of the WW1 BM badges (not every one!) listed/recognised as being applicable for this process. As always ,there are exceptions( unofficial ?), but not BW evidentaly. Seems that WW2 Canadian are the only possible 'real' examples known there.
Cheers !
Steve