JD, I do have a Springfield, but it came lightly-used with two mags. One was a Colt mag, one a blank one with markings. At a recent gun show I picked up a second Colt mag for $13 or $14. If my memory and logs are right, this is the gun show mag.
Like Jeremiah mentioned, both of the Colt mags (authentic or not) have the four little welds holding the floor plate to the mag body.
Counterfeit mag eh? Why didn't I think of that...