50 BMG

Does anyone have experience with Alliant Reloader 50? I plan to resize some pulled 639 grain API bullets and use Reloader 50 as powder / propellant. The closest reloading data from Alliant is a 650 grain bullet; powder load is 255 grains of Reloader 50.
I believe that the WC860 is from pulled surplus military ammunition; I have read that this is preferred when using APIs, as it is far cheaper, than other new commercially sold powders. The APIs that I have, all have serious tool marks from pulling; as such, all need resizing. Most of the supposed 639 grain APIs I bought are actually 649 grains. I did some research, the 639 grain APIs seem to be are the older version of the M8; the 649 grain API are a newer version. Identification can be determined by weighing and also by the cannelure; one is cut and the other rolled.

Does your WC860 completely burn? I have read residue and unburnt granules are present after firing? Have you experienced that with your batches of WC860? I have also read that APIs are not that accurate.