Defiance medium action is the same as a Remington short action not sure why they named them like this.
They did/do a Model 7 clone which they called their short action, so the Rem 700 short action footprint version became their medium. I can't see the M7 version on their new site though.
The XM looks like a nice concept for a short magnum, particularly with their custom ADL box and follower.