I use the South African magazines for my Hi Power. They do stick out a little, but not that much. They are advertised as 17 rounders, but they fit 15 reliably.Not sure about extenders but there are 15 and 17 round magazines available, or at least there were. I had a few but sold them off. The 17 sticks out maybe 3/4" from the bottom of the grip frame. They worked well, I can't remember now why I sold them. I remember hearing that they were South African manufacture but that could be nonsense.