My solution to Foster slugs is to leave all slugs and slug guns in the gun safe....... but I would probably still work the project if I was to do it again...... a person gains great knowledge ....and, a good dose of humility by doing such things.
And I still wonder how the rifled screw-in chokes really work....hmmmm....another project?

BTW, I wish I could take credit for the tooling, but it was done by a real machinist at a local manufacturing firm.