A million years ago I was a member of the American Cartridges Collectors now called the International Ammunition Association, Inc. who can be reached at
http://www.cartridgecollectors.org/When I disposed of my shotshell collection there were a bunch of wire wrapped shot concentrators. One of the journals (this would have been over twenty years ago did an in depth article on them. When I got out of all cartridge collecting I disposed of the old journals as well, I’ll bet the new origination could help with research.
