FIT FIT FIT! And after that, FIT!

Hardness does come into play, after that. .001" to .002" over bore or cylinder throat size is key. If you have a bullet that is a bit hard, 18+BHN, you can get good results by using a bit faster powder and pushing them to the upper end of the respective data.

Case in point, Bullseye over H110/W296. Pressure is higher with the first and lower with the later.

Been there done that. Works!