The 9mm is an auto pistol cartridge, and as such is in its own field in such a firearm. Its a hot cartridge but loaded with a fairly light weight bullets, going, as I recall with a 124 gr. FMJ bullet, often with a 115 gr. bullet.
The .38 Special, on the other hand has a much less impressive muzzle velocity, but usually is loaded with bullets of 140 ~ 158 gr. in weight. And usually with a lead bullet of JHP.
If you're asking for a defensive round, I'd go with the .38 Special with a lead Semi-Wadcutter bullet.
All of the foregoing regardless of barrel length. The powders used for the 9mm aren't going to be affected too much by length, and some .38 Specials are specificially loaded for the shorter barrels.
Between the two, I'd go with the .38 Special, hands down, regardless of barel length.
I saw the .357/.38 Blackhawk has an interchangeable cylinder for 9mm, and I wondered how the 9mm would perform in that revolver with the 4" and 6" barrel lengths, compared to the .38 (I know there's no comparison to .357!)
No special reason; just curious. I don't see myself using it for SD, for mainly for plinking and varmint shooting.
I see snub-nose revolvers (2") chambered for 9mm, and I wondered if there was any performance reasons why it would be chosen over a .38. I can see the cylinder and gun could be shorter and therefore lighter compared to .38....
Why 9mm in revolver? Because I have three 9's. Thought a revolver would be easier for my wife to shoot, since the slide is hard for her to pull back.