What case is 458 socom based on?
Can you make brass out of anything else or is it its on deal?
It is pretty much its own deal. Unless one has access to ultra cheap .50 AE parent case* and a good lathe to reform the head size to that of a .308, making your own .458 SOCOM brass is a money looser, especially considering how cheap the Starline formed brass is.
*the .458 SOCOM is not made from .50 AE brass, but the parent untrimmed case used to make the .50 AE, and how one would get hold of that case cheap is beyond me.
Isnt it longer than the 50AE?
Yes, that is why I said it is based on the parent case of the .50 AE, not ON the .50 AE. The .50 AE is drawn out on the presses a lot longer than it is in its finished state. Then it is trimmed back to the finished length. The .458 SOCOM is based on the longer parent untrimmed case of the .50 AE and then not trimmed back as far. The head size is also altered to the .308 head size.
Buy 423 Westley Richards brass ($4 a pop), cut it off, form it, trim it and turn necks ...
You can get 500 Linebaugh Long, 500 S&W or 50 Alaskan brass, form it, trim it, then turn down the rim on a lathe and cut an extractor groove
OR (and I can't believe I am going to say this)
You can get .50 Beowulf brass, form it and trim it and use a 7.62x39 bolt ...
For TRUE .458 SOCOM brass, you have to have a 0.473 rim size, which is larger ...