cm9 and cm40 magazines

[Rmkeyjr]

I own both. The magazines fit interchangeably between the 9 and 40 pistols identically. Further the 9mm round fit the forty and the forty rounds fit the nine magazine. If one is not very careful and loads a 9 in the 40 bad news could follow. I am surprised the mags are totally interchangeable. Has anyone else noticed this?

[McE]

The difference, if there was one, would be the feed lips. Simply 'fitting' is not an all-clear to say they are totally interchangeable.
Since you own both, you can be the guinea pig to test for function, which is the only useful bit if information concerning interchangeability.