I have thought about a 9x39 on my mini-Mauser 223. Sounds like fun using the improved case and a 180 gr Barnes X or a hard cast WFN. Looks like a great gun for fun and compact, easy to swing full stock. Reminiscent of the old Steyr M/S. Be Well, Rustyzipper.
Ive done a couple 338 x 39 on AR and CZ platforms, lots of fun but I like my 375 Grendel a bit better.