I’m helping a new collector identify some 7.62x39mm cartridges he recently acquired. He has a Soviet 7.62x39mm PS ball cartridge, copper clad steel case, head stamped “17 59”. It was identified by the previous owner as having “Pyroxylin” powder. I have not heard of this before. Is it just another name for the WUFL powder normally seen in Soviet 7.62x39mm?