I once read about a wildcat called the 243 Catbird that was based on the 270 case. Has anyone had any experience with this round?

6mm,
I can supply you with the case dimensions and a drawing. Email me your address at ed@aement.com.
Regards,
HockeyPuck

Yes, agood bit of it. Don't waste your time, too much effort for too little gain. Go with the 6mm-284 much easier to form cases and deliver the same velocities.