Brass doesn't seem to be a problem. I picked 100 ea. and they look like NEW. Figured I'd get brass and go from there.
One of the Guys on the Small Caliber Club forum seems to be the "Go To" man for brass. Pretty interesting little round. I think the 4.6X30MM is the same as the 5.7X28? Just neck it down to 17. OR, if you're feeling like trying something different, try going to 14 caliber.
Big jump in bullet size from 30 cal or 6MM to 20. Then, try going to 17? I thought handeling the 20s was a chore? The 17 should be a real challenge! Some of the Guys are pushing 20 grain bullets to 3800 + FPS with deadly accuracy.