Very popular are revolvers chambered in 9MM cartridge (aka 9x19, 9MM Luger, 9MM Parabellum).  The case dimensions are defined in the SAAMI specifications.  LINK

The first dimension to notice is the extractor groove diameter.  It is specified as 0.347" +0/ -0.020.  That's a wide tolerance.  And that's the key dimension we use for the moon clip to hold the rounds.

It's perhaps a perfect dimension and tolerance for extracting the cartridge from a semi-automatic pistol.  But we're trying to hold the round in a moon clip.  If we size the moon clips to fit the 0.347" dimension then the 0.327" (347-020) would fall out.  And if we size the moon clip work well on the 0.327" dimension then the 0.347" case would not go into the moon clip.  I predict some cartridge manufacturer will make a 9MMR case specifically for revolvers.

At Revolver Supply we attempted to pick a dimension somewhere just below the 0.347".  We are finding most of the market approves our choice.  But.................and there's always a but.  

Some competition shooters want a tighter fit.  For those customers we make thicker moon clips (our extreme moon clips are 0.040" think).  We now fill up the extractor groove and hold the rounds with NO wobble.  Good news.  But some bad news is that we took away 0.005" from the back of bullet to the frame clearance.  In the real would you might find some rounds when used with the extreme moon clips that do not freely rotate in the cylinder.  Most shooters just set them aside.  We'll gladly send out samples of any of our moon clips for you to check.

9MM Range brass.  When using range brass or any brass that was shot from a semi-auto with an unsupported barrel (can you say Glock along with most others) you will have a bulge in the case.  You need to be sure that you take out this bulge when resizing the brass.  I use a Lee 9MM resizing die and that works as do many other resizing dies but check with a case gauge.

Look again at the SAAMI drawing for the 9MM.  You will notice that the 9MM case walls are tapered.  Be sure you're using the proper resizing die for 9MM cases.

As a shameless plug for our products, we make moon clip checkers and these are made with a proper 9MM taper for checking assembles moon clips.  Check it out.  LINK

Fimally the 7 shot revolvers both 9MM and 38/357 have the rounds so close together that only one unloading tool that I know about will work without bending the moon clip.  Why ours of course  LINK