Me - If I were making one for myself.
I would take a 3" long piece of ½" A360 Brass, Thread the end ½-28, 3/4" long then drill 3/8" dia. 2.5" deep. Now reverse the part in the chuck and drill through with a 11/32" drill (.344).
With a small boring bar, bore like .383" or whatever it takes for a slightly loose slip fit for your 357 case that has been cut off 1/4" or more from the head about 1/4"- 5/16" deep. Use good old 50/50 or 40/60 or 60/40 soldier to sweat the case in the bore.
From the threaded end - use a 23/64" ream to open up the area between the 3/8" dia. and the case ID feeding into the case to remove any soldier which may have wicked through. I would not go into the case more than about 3/16". Cutter is now done.
Now fab a handle to fit the ½-28 threads from AL or brass or delrin or... if the threads don't go through then drill 3/8" through.
Took longer to write it up than it would to make it - except I think my Acetylene bottle is nearly empty. - But then I understand not everyone has a lathe (or 4) in the garage.