I've done some googling for beretta and hi power 30rd mags. From the images that show up they are almost identical, but both have features this one is lacking. Every 30rd 9mm mag I've been able to find that comes close to this one has an indentation near the base on the sides. Most have bullet counters on the back. Since this has no markings I wonder if it's an aftermarket mag.
Some additional information; I think this comes from a 9mm carbine that my former brother in law owned back in the late 80's early 90's (for sure preban since he didn't buy any guns after the ban in '94). I remember talking with him a long time ago about how he used to have a problem getting 9mm ammo for his carbine since every place wanted to see his pistol permit. I can't for the life of me remember what he had, and it's next to impossible to talk with him anymore.
I will try it out in my Beretta at some point to see if it feeds, if it works I'm just calling it a Beretta mag, if not then it's something else, but I would like to know who made it.