WTS New, unused CMMG chamber adapter assembly with protective cover, $70 shipped CONUS.
You can use it on a 5.56 upper by borrowing your existing .22 bolt and frame from a dedicated .22 upper, or you'll need to buy a .22 bolt and frame assembly (minus the chamber adapter and cover).
Here is what I'm selling:
Chamber Adapter Assembly, 22ARC, Bravo
Cap, Protective, 22ARC