Where can you find these that aren't priced at $100.00+?Yep that is exactly it.
Am I remembering wrong - I thought I remembered there were 3 variations of mags for 4506 and not all interchangeable - I think I have 1 marked 4506-1 only somewhere in a drawer.
Has the recess along the back left edge for compatability with magazines that have the vertical cartridge-holding indentation. And the back right edge has also been changed/improved.