What you should have asked
Weblance,
I think the question you should have asked is, WHAT DOES A 9m.m. REVOLVER DO BETTER FOR ME THAN ANY OTHER CALIBER? If you had asked that question, you would have your answer,
Do I get a more powerful gun if it is chambered for 9m.m.?
Answer, it depends on your load and the gun. If the gun is a small frame (say a 5 shot J frame or COLT D frame size), you get more power from a standard 9m.m. than a standard .38 Special. If you compare +P .38 to standard 9m.m., I think the difference is not worth worrying about.
If you up the ante to 9m.m.+P or +P+, then you should compare to the .357 magnum. However, both will recoil too heavily for me to shoot accurately and I think most people will skip over a J-frame loaded with .357 or 9m.m.+P+ after just a few rounds.
As I said, I have one of the nicest 9m.m. revolvers ever made, the S&W 547. It shoots very much like a S&W model 13 loaded with ,357 magnums. So why bother.
Most people either buy a gun because they need one, like for a house or car gun or for CCW or they buy because they are into guns, either for using or collecting. That leaves the 9m.m. revolver in a small, niche market.
You may notice that the wonderful, super perfect revolver round (at least it is according to some gun writers), the ,327 magnum is not burning up the market. It should be popular, but it may never sell any better than the .32 H&R magnum because it is a round for a GUN PERSON. Police departments are not buying it, nor are military or government agencies.
If the FBI or BORDER PATROL or MARINE CORP adopted a 9m.m. revolver, it would undoubtedly become much more popular.
Ask yourself, what does a J-frame, 5 shot 9m.m. do better than either a .38 Special (with reasonable recoil) or a .357 magnum J frame do?
I asked myself this a long time ago and now I carry a .380ACP SIG 232 when I am not carrying a holster gun.
Oh, the one thing a 9m.m. revolver might do, is offer a more compact revolver than a .38 Special because of the overall length needed for the cylinder and thus frame length.
TAURUS has announced a .380ACP revolver. It uses a short cylinder and short frame to reduce size and weight. If it catches on, maybe a 9m.m. revolver might be produced. Then we could see if it stands on its own merits.
Jim