I just received my big stick in the mail today. I ran out to the the range for a test. I was able to load 29 easily, seating the mag took a whack and cycling the slide was like molasses in winter, but it is brand new. Range test was perfect, match tomorrow will tell the tale.
A small frame CZ 170 mag is possible using a Promag body, a Grams spring and a plus one base pad. About $70.