Also I think the 645 magazines have a steel floor plate while the 4506's are plastic.
Not that it matters with functionality, I just though you should know.
I've not had any problems with Numrich and I have ordered quite a few parts from them over the years. Any day now I should be receiving a new magazine follower for my 4506. The original one was broken in such a way that it would not lock the slide back on the last shot.