In March of 2011....
I had Kiff & Co make a reamer based off the 6.5 Grendle necked up to .308. You could very well describe it as a 7.62 x 39 Improved.
It has the same subsonic capabilities as the original 300 Whisper but ran away from both the 7.62 X 39 and the Whisper in upper end velocity .
That said, the 7.63 x 39 is a pretty amazing cartridge given the performance you can wring out of it by handloading.
