John makes a good point, but this is also my thinking in why I would not put a 3913 slide onto a CS9 frame. If the bottom lug on the slide somehow struck the aluminum frame and gouged (or possibly cracked) it, there's no getting a new one. And I would hate to think of something getting caught in the gap before firing as well...

As I mentioned in another thread on this subject, a 3913TSW pre-rail or a flush-fit, 7-round 3913 metal base plate magazine both achieve the same effect in a much safer manner. And I have both in my collection.