Did you try cutting the case down at the shoulder to see what velocities you would get without having to expand the necks?
I havent read all of the posts, sorry if this was asked,heck there are so many.....
I am not a reloader, just wondered if that was also feasable, or if it didnt improve much over a 3"
Thanks for your hard work.
Makes me want to shoot my High Standard Bolt 12GA.