Do you reload?
Just get Polywad spreader inserts one gauge smaller than the shell intended. For your 16 order the 20 gauge inserts.
I use Polywad for my mod / extra full 12 gauge to shoot skeet, sporting clays, in the field, and works great.
My opinion... Keep the bores original.
http://www.polywad.com/spredr-inserts.html