I'd bet my left gonad they are not GI mil-sup left over from WWI or WWII!100 blue military surplus moonclips for $30 at OLD SARGE'S
I bought a bunch of blued ones at a gun show last year that turned out to be soft & thin junque, so I know they are out there!
Just to clarify, the ones I purchased from Ranch, 1/3 and full moon, are inexpensive but a quality product.