in my search for a longer case with the sme rim as the 7.62x39 I found this tid bit of info. HMMM
seems guys can make this round from 7.62x39 about half way down
Looking for a Longer Case with the Same Head Size as the PPCs and 7.62X39 - Shooters Forum
also mention a 444 rimless from 30-06 brass (were did we hear that before) This need to be checked out also shows some other rounds with a very close rim dia.

Need info on .401 Win. SL - Cast Boolits