To your second point, I forgot about the 22-250 case. Probably a better place to start if you are ok with using a large primer.
22-250’s got quite a bit more case body taper, which may - or may not - cause issues when trying to push shoulder back enough. This was a problem years ago before factory 6XC brass became available; common practice was to use 22-250 as parent brass for 6XC. I got frustrated with availability as much as case life, why I ventured making it from Lapua’s Palma brass when that appeared in what, 2010?