Thanks, and I'll look though a copy of Greener.

Wright says he often resorts to a duplex charge of 4759 below the main BP charge in order to get enough fps to regulate.

He mentions tests in which old BP cartridges were tested for fps, and they were found to be correct. One cartridge was pulled apart and its powder tried with modern components, and again the fps was correct. It wasn't, though, mentioned what the granulation appeared to be.