Since this is something of a perennial subject, I dug up an old thread with plenty of useful (well, interesting at least!) guff, including my experiences with CV-joint ball bearings buried in there somewhere.

Shotgun Slugs (...again!)

Hope it is of some interest.

I should add that my hopes and expectations for the then-new RC4 shotgun slug were not realized, to say the least!
Long-winded account of my field results can be viewed here, if you've got the time to trawl through it!