Trimming .38 Super sounds like the best way to go, as you'll never have to worry about running out.
I made brass for a 9mm Japanese revolver by trimming .38 Super, which required trimming off only 1mm, but I still had to inside-ream the cases to seat .357" bullets. It was a bit of a hassle, but after I had 50 useable cases, I didn't think I'd have to make any more.
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