I have 2 of the MCA adapters for .22lr in .223rem and .22wmr in .223rem.
They are fun to play with, and come in handy once in a while, but have there drawbacks. They are kind of a pain to load, and knock out the spent case with a wood dowel or similar.
I had an older slow twist rate NEF single shot .223 that shot .22wmr pretty well, and .22lr ok. My AR's and boltguns dont shoot them very accuratly.
I keep a .22lr Super Colibri loaded up in the .223 adapter for the occasional rabbit or such that jumps out when a full power .223 would be too loud.