The SASS rules regarding revolver calibers are:
- Must be centerfire calibers 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 caliber 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.
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. 26 - 2022