The x39 case with the taper blown out is available in several calibers, the first and most popular being the 6.5 Grendel which has commercial brass available. There are variants from .22 to 35 caliber, but the Grendel is the only one with dies and parts available off the shelf I am aware of. I have a reamer for a 30 Grendel Imp 40', but haven't got round to the project yet. Dies will be expensive unless I make them. Seater is easy, sizer, not so much.
I have a 7.62x39 in an A4 configuration and have had no problems with ten round C-Products mags so far.
Last edited by gzig5; 09/25/15.