I apologize for the lateness of my reply, I have been absolutely swamped with ammo orders. These guys have nailed the answers. I have tried this as well, shooting 9mm jacketed and cast, and found the results to be effective enough, but in the case of longer range true precision, you need to match the projectile size. For the vast majority of the closer in, 15 yard A-zone type stuff, it was sufficient.
The .38 Short Colt really is a nice little cartridge and it has been one of the better things about the shortage of components. Taking pages out of history and adding a modern twist has been pretty fun, not to mention quite effective.
Didn't read all 15 pages but I think I saw this mentioned; "rimmed 9mm"; https://www.rccbrass.com/9mm-federal/
I shot 50 more rounds today. I went out as far the pistol range goes 15 yards and other than a few bad trigger pulls (I jerked the trigger), it still shot amazing.
I then switched to 158 grain 38 Special. The POA/POI was exactly the same as the 125s in the short colt cases. I am pretty happy!
Today I tested a bunch of different loads out of a Colt King Cobra 3-inch. 357 Magnum, 38 Special, and 38 Short Colt. One of the 38 SC loads, 125gr JHP with the equivalent of a standard pressure load of BE-86 for 9mm, gave one of the two best groups of the day. Other variations, mostly heavier coated bullets and various powders, were mostly acceptable.