I certainly will try your method, KISS almost always works better. And I don't think I'd use anything less than 1F granulation in these huge cases (.577 and .577-450 are my largest cases and dwarf my .50-70 in capacity).
I could be mistaken, but I believe that those who I consider knowledgeable (e.g. Douglas - Double D) have never claimed the COW was burned. My understanding is that the BP mixed with the COW prevents the COW from clumping and results in the COW being ejected from the cartridge case as granules.
Ed