Thanks for the interest in this idea!

Really not interested in an ar build, just not my cup of tea. For what's interesting about an idea like this bolt action is definitely the way to go.

338 Federal would be a step in the wrong direction, looking at options that maximize subsonic accuracy/performance- moving up in case capacity would be counterproductive.

The 223 parent case makes everything easy. Sure you have some initial trimming/forming but then you're g2g. Cheap plentiful cases and no need to modify a bolt face like with the spectre. Headspaces off the mouth- why not? Get everything set up it isn't that big of a deal. Being able to run a repeater would be great but not a deal breaker, glad the BO guys aren't having any feeding/extraction issues.

Major downsides seem to be bullet selection, especially with cast options. Will keep looking to move forward with this idea but not married to the case, thanks again for the replies.