Grendel doesn't use the same bolt - it uses a deep face x39 bolt.
BCG doesn't change for any of the AR compatible cartridges, except for the WSM's, 9mm, 22LR, only the bolt itself.
I wouldn't get too hung up on compatibilities for bolts, barrels, and magazines. Unless you're shooting bargain bin, mil-spec barrels, if you change cartridges in an AR, you'll have $250+ into a new good quality barrel, even if you use the same upper, plus cost of ammo. Buy a new upper, and you have $300-1,000 into a new upper. Adding $75 for a new non-223/5.56 bolt and $50 for a few mags isn't a big deal in the scheme of things. I have or have had AR's in .17rem, 20prac, 204, 223/5.56, 6x45, 243wssm, 25wssm, 6.5g, 6.8spc, 300blk, x39, 450b, 458soc, and 50beo - swapping barrels, bolts, and mags really isn't a big deal as long as you stay away from the proprietary uppers and extensions in the oly/dti WSSM's (only because nothing swaps on those, as the upper is a completely different platform in its own right).
The 7valkarie is an impressive cartridge, and honestly does seem to maximize the potential for the AR platform - with no news on bolt thrust long term effects yet - but as I'm getting set up to build one myself, without any offense intended, if you're asking a question about which cartridges share a common 223/5.56 bolt face, the 7VAR is not for you. Making cases alone is a huge undertaking, so it's really not something for the average reloader and average AR owner to mess with. Even as impressive as it is, and being set up with all of the equipment to fireform, neck ream, neck turn, shorten cases, and many years doing so myself, the 7VAR is a HUGE pain in the butt for what little benefit it brings over some commonly available cartridges for the AR, let alone when you start talking about slipping up to an AR-10/LR-308 platform, where the 7VAR gets smoked by a handloader using standard brass and cheap factory dies, and matched by factory ammo... It's a BIG undertaking for such a small gain. It's a little better than the 6.5grendel, but not so much better the average shooter will be able to tell the difference, other than telling the difference between buying ready-to-load 6.5G brass and spending a few hours building brass for the 7VAR.
