After I measured all the bullet engagements to lands/throat my hunch was confirmed--certain bullets with their "fat" parts of the ogive forward prevent them from being seated at a SAAMI "standard" of 2.26 for a comparable grendel cartridge (and even a few of those are seated shorter depending upon the manufacturer.) Harrison at ARP specifically designed the chamber to handle high BC/SD bullets with "longish" tapering ogives--like the ones commonly found on berger bullets and matchkings. My first crack at a wildcat--I'm learning why they are called that.
Here is my first group of reloads for development using berger's 95 gr VLD. Unfortunately, I forgot to get their hybrid VLDs specifically made for AR's--their regular ones often have feeding issues in AR's of any caliber in my experience. Hopefully it will work out.