What about a custom mould in a heeled bullet design, like the old 38 short Colt. That portion of the bullet to be seated in the case was of narrower diameter than that above the canelure. I picture a big 155 - 160 grs RN with couple of lube bands above the heel, soft lead, sized to groove depth with a short heel that allows you to seat at case diameter comfortably. Keep 'em soft, stick to 2000 fps and less. Interesting.