Spent some time over the Independence Day weekend knocking out the barrel nuts! I machined them from pre-hardened 4140 (~25RC). I ended up making like twenty of them. If there's interest, I'll make more for sure.
Technically, at this point I can assemble the rifle with the 54r barrel and shoot it! I still need to machine the new bolt heads and make a new interruptor before I can fire it with the actual 8.6 BLK barrel, however.