Hope all goes well with the wife's fusions! My 4 neck fusions, well 1 of the 4 didn't go so well (C2 to C3). AND hopefully you'll get back to shape in no time!
When some barrels are proofed to 100k+ you just need to know what you're getting. Chamber will be the thickest part so mo worries there? I haven't seen the sig cross design or others that produce firearms for 80k usage, but have seen the bolt and extension design on the 277fury AR...
From reading about this brass some thought there was agas leak where the 2 are joined and others had some kind of ring in the throat at neck. IIRC all have been tested in a BA and not in semi's?
I downloaded to 65k as the barrel/bcg/extension isn't 80k rated. I have an AR in 277fury, but haven't had time to finish the build along with the other AR's from 4 years ago. I think on LRH there's a thread about the hybrid cases as some neck to different calibers to meet their wants...
I do have a pound or 2 to try, but haven't had time in 4 years to reload. I'm more than that behind on shooting everything I've built since '19. Next year is upon me and hopefully have lots of time to play! New powders I've bought and haven't tried yet are all 3 sta-ball, grand, 15.5...
I don't know what you'll kill with that groupings..............well everything across all dimensions........no esc-a-pe for them.
A funny but stupid fact about me is I'd been shooting 264wm since I was 10 (almost 11) yo and was scared of the 308win thinking it would just recoil like crazy...