turn 223 into 300 blackout?

[Hoser]

I have made 30-40K pcs of 300 BLK and 300 Whisper brass since the 300 BLK hit the street. No complaints yet. Well actually thats not true...

I turned 1,000 pcs of brass into 300 BLK for a shooter in NM. He tried to load it using a bad batch of Forester dies. Not his fault and not mine really. But it was a complaint so I want to be completely upfront and honest about that.

The main difference if the throat, not the chamber itself.

300 Whisper/Hush/300-221/WTF and 300 BLACKOUT go and no-go gauges are the same.