There seems to be a pattern here two people on this forum having the same trouble using VLD bullets and Alliant powders .
Two people is not exactly a big sample but it is interesting.
Reloader 17 is a new powder and this is what German Salazar and Bob Jenson said about it Alliant Reloder 17
Is it possible that due to the altered burn rate and different chemical characteristics of this powder that neck sooting with VLD bullets is more likely ?
They say that the burn rate coatings are infact through the powder grains not on the outside so could that mean that the powder is more prone to dirty burning ?
They say that the powder pressure curve is sharp to rise but slower to fall so could that mean that a long barrel is required to get the best from it ?
Anyway I think you should test some other suitable powders just to see if the neck sooting stops, Sorry I can't advise another suitable powder because I don't have a listing for R 17 and can't find a burn rate equivalent for it at the moment .