Why do expansion when fragmentation at subsonic velocities has already been proven? Make a .30 cal version of the bullets in these:
RCECO has a nice note on making pre-fragmented lead bullets:
http://rceco.com/img/RSBook3.PDF
I have dissected the CCI bullets and they are segmented with 0.080" depth (1/3 or .224) cuts on the
outside of the bullets. I suspect that the cuts are on the outside because the segmenting is done to the lead wire while it is still in the spool. That would make sense for mass production. Then bullets can be made from those spools on existing equipment.