I would bet new brass will not be a problem. The Saum is a 65,000 pressure round and when you start to get deeper into case life, I believe web expansion can start showing up. I have a 300 WSM that does same thing in 6-8 firings on Hornady brass. I just accept the web expansion as part of the short fat cartridge characteristic. I have just never had long case life with WSM's and bet SAUM's can be the same. If you are shooting these types of cartridges in upper spectrum of loads, I bet the webs do not last. Just my experience with them. If someone can show me how to get more case life out of them without sacrificing performance, I am all "ears"! I've even tried to get a small base die but did not find one.
Sounds like you are confident there is no carbon buildup in throat.
Sounds like you are confident there is no carbon buildup in throat.