Say it ain't so Don - 'ya mean there is no magic!?! wink

What about the Herb Orre choke?

[Linked Image from photos.smugmug.com]

And the "Multiplied Choke Bore System"?
https://members.boardhost.com/lcsmith/msg/1624920858.html

Gough Thomas, Shotguns & Cartridges For Game And Clays, 1970
"Occasionally, a clay pigeon shooter's outstanding success at some major international competition will be attributed by him or others to some marvellous new system of boring. This is a subject that is in every way likely to involve elements that have nothing to do with practical ballistics; and in view of the fact that every conceivable variation in the boring of shotguns - every possible combination of features - appears to have been tried, one is entitled to treat any such accounts with reserve.”

Previous choke length thread
http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=466257

Another resource "Making Shotgun Barrels" by Harold Hoffman
https://archive.org/details/Making_Shotgun_Barrels_By_Harold_Hoffman_Action_Book_Publishers/page/n1

https://sites.google.com/a/damascusknowledge.com/www/home