have you ever tried a hollowpoint bullet with "fins" inside of the hole?
I have read about those in old gun magazines,
to get them spinning while shooting out of smoothbores
from the time around the paradox gun when they tried to combine shotgun and double rifles
IIRC it was this dude
http://www.germanhuntingguns.com/Sec...ID=1&Tag=Stend
edit found it
http://iaaforum.org/forum3/viewtopic.php?f=8&t=7561