I didn't pay enough attention, put the router plate on backwards after removing to clean out chips, and managed to machine through to the mag release button cavity. Oops. I decided to try finishing the lower anyway and seeing if I could make it functional, and proceeded to snap the end mill that I was using. Of course, most of my tools aren't with me right now and I don't have the right size wrench with me to swap to the other end mill that I have.
The top plate is almost symmetrical so I didn't realize that it wasn't, hence the angle and screwing up the lower. Would be nice if it was symmetrical.