I have what I think is a factory High Power high capacity magazine. There is no stamped ID on it but it has a polished blued base. The follower is plastic.
Is my magazine factory? It looks just like my known factory magazine.
Do any after-market magazines have a polished blued base?
CDNN is currently selling an identical magazine as factory Browning, so I'd say yes. Other aftermarket magazines have blued bases, but are not done in the phosphate finish as you have.
The funny thing is I have 2 FEG Hi Power clones, and the magazines that came with them are identical except for the followers. Weird!