Alright guys, got an email from Mark this morning...here's the official update:
Thank you for reaching out and letting me know about the forum. Just incase anybody asks you, here is the official update.
We have a working/firing/feeing/extracting/ejecting prototype, we will call this our Rev 1 223. We are working on a new Rev 2 223 conversion that is doing everything Rev 1 223 conversion did, but better. The Rev 2 conversion is not a firing version at this point however. We are getting some made up in the next week that I will be able to fire and I will post some videos shortly. We also have a few high capacity magazines that we are working on at the same time.
For the 300 Blackout. I'm having trouble making it work 100% of the time due to the short nature of this round. Short 40 gr 223 rounds feed great and the longer match bullets (69-80gr) feed even better.