As far as I know, Kreiger does not have a prohibition against using SS for smaller profile barrels, they do however use a different type of SS for them (410? which is 416 without sulfer).
SS is oft maligned and misunderstood... most of the SS you run across in your life is austenitic and is normally very resistant to corrosion, but also prone to cracking (cloride stress) and is often offered in a ductile -- seemingly soft -- state.
Keep in mind that SS was developed for military barrels, but the high carbon steel that was used early on made the SSteels of that day very brittle... today, we have available martensitic (400s) SSteels that rival many tools steels and are the choice for durability in many applications. Also, there are the precipitation hardening SSteels, I would challange anyone to show how a PH is inferior to a high carbon steel in an way? I have worked with 17-4PH to make several gun parts and consider it to be one of the top shelf steels available -- but then, it is also expensive