It's gonna be tough to get the 223 to subsonic while still having enough port pressure to run the action.

Another option is a CMMG 22 Rimfire adaptor. My 1/7 10.5" did reasonably well with 40gr Federal Target, and Aguila 60gr subsonic. Didn't like CCI Velocitors.

[Linked Image from i.imgur.com]

[Linked Image from i.imgur.com]