Yuma
normally the best overall is .001-.002" larger than groove diameter, for nitro powders.
BP loads, totally different animal to skin.

This should answer all you questions in regards to coating & lube etc.
Homer did a really good tutorial on it quite some time back, if I find it I'll post it up again.
Hi-Tek coatings, here in Oz.
https://hi-performancebulletcoatings.com/about-our-coatings/