The SASS rules regarding revolver calibers are:
- Must be centerfire cartridges of at least .32 caliber and no larger than .45 caliber or percussion calibers of at least .36 caliber and no larger than .45 caliber.
- Must be in a cartridge commonly available in revolvers. Examples include, but are not limited to, .32-20, .32 Magnum, .357 Magnum, .38 Special, .44 Magnum, .44- 40, and .45 Colt. (Includes some semi-auto pistol cartridges, e.g. 9mm, 10mm, and .45 ACP)
SHB p.37
Since Ruger, Colt, and other revolver manufacturers have been producing revolvers in "rimless auto pistol" calibers for many years (including a number of convertible models in 9mm, .45ACP, 10mm, and others), single action revolvers in 9x19mm are LEGAL in all categories except for "Classic Cowboy/Cowgirl" (which require .40 caliber or larger, rimmed cartridges).
All ammunition regulations apply (SHB p.26)
Here is a link to the Shooters Handbook
Shooters Handbook Vers. 27.4