sorry, but I do not understand your subtle difference between “finished at MEN” and “finished by MEN”. Could you be so nice to elaborate?
Apart from that:
As far as I can tell, for a manufacturer of brass cases it is a really big retooling job to set up a steel line. For example, the heat treatment furnances for brass normally cannot produce the temperatures needed for steel. The presses wear out much faster.
Unless a government is willing to pay a lot for this change (France 5.56 mm, or example) I do not see how a manufacturer outside the former Eastern bloc could make any profit from it.