Ruger's main idea/reason for this combo was to have one, if not THE most versatile revolver in the world.
With the .38 Special/.357 Magnum cylinder AND the 9MM cylinder this revolver is a shooter anywhere. In other words, ammo IS available..
You will find that cast (lead) 9MM loads will be the most accurate in your revolver. Your revolver will have .3565"-.3575" bore diameter. Cast 9MM bullets are usually .356" diameter.
FWIW: I cast bullets for my 9MM semi-auto pistols, and I lube/size these bullets to .357" for the best accuracy.
Hope this helps..Bill.