Lots of folks have gone to Hevi Shot a revolutionary nontoxic tungsten-nickel-iron alloy developed by Dr. Darryl Amick of Albany.
And it does require its' own special choke tube - as an extra full normal turkey choke tube is far to restrictive.
I have not tried Hevi shot but you can find lots of topics here on a search. The main reason I have not as I have no need - AT This Time. I can still use my Winchester Supreme copper plated #4 in the various states I hunt.
JW