I haven't seen ball 'slug up' to groove diameter in my bore rifles, no matter the rifling profile -- but I haven't shot or owned an 'invisible' like the CH, Lancaster, or Tolley Ubique.

I'd try a thou (or a few) under major diameter and work with the wad column.
Fiddle with lube.

I can't wait to see how it shoots when you get it running.

Cheers
Tinker