[ERA Chas]

If they are oxidized green/gray, have the valve stems outside the cast webs, are about 5-8 pounds each and say 'Cobra II' on them they're real. They would be 7 1/2, 9 1/2. Aluminum repops from Trigo, Vintage or PS would not be oxidized, have stems between the webs, be noticably heavier and have different face contours.
Magnesium will oxidize in one to two weeks depending on humidity and dampness - unless you polish as often. See my gallerey.