I doubt very much that any damage resulted. Brownells actually sells a tool specifically for this purpose that works basically the the same way, though a bit more precise. I have it, I've used it and it works great - no damage to my mags inside or out. You simply exert just enough pressure on the base of the magazine to allow the base plate to be removed. Finger pressure seems to work fine for most. Wanna kill these ads? We can help!