There were steel headed, brass bodied .30-06 cases made at one time. The thought was that cases usually fail because of primer pocket expansion. The pieces threaded together, and so the head or the body could be replaced. The brass portion of the case was drawn, not lathe turned from stock. brass rod/pipe, etc. has different metallurgy than drawn brass.
Composite cases would likely work with reduced loads. I'd be queasy about full loads. As far as that goes, how about an adapter that would accept a .50 case necked up to 14.5?
Dies, adapters could certainly be made on a lathe. But it would not necessarily be easy or inexpensive. If I had a PTRD, I would certainly be spending time at my lathe. But If I had one of these rifles, I think I would be changing the barrel.
Years ago, when the Lahti 20mm guns were available and cheap, I heard of a couple of guys who had one and worked at an auto plant and had access to the tool room there on the night shift. They made loading dies, and rigged an automatic lathe (this was long before CNC) to make solid copper projectiles. Cases were repocketed to accept .50 primers.
Where there is a will, there is a way.
