Magazine manufacturer?

[Garandrew]

B in circle? Used by what carbine manufacturer?
Was U, the Union Hardware used by WRA?
My WRA's have IW, BW, plus I have U, IU, IA's as extras.
Some have large holes at rear lower end of box, some have flat bottoms with drain hole, others have crease at bottom.
Which ones besides IW, and BW were WRA contractors?
Andy

[cafdfw]

I believe these are correct:

B in a circle was Bridgeport Metal miscelaneous replacement mag.
U Union Hardware miscellanous replacement mag

UW was Union Hardware used by WRA

IU International Silver for Underwood

IA Autotyre for Inland