Along with the size of the grains, it helps control the rate that the powder burns....Robin
I would not put a lot on money on a bet that it controls burn rate.
There are a number of factors that will effect burn rate but graphite is not one I remember hearing though since the polish on ungraphited powder does slow the burn rate a little its possible. Its primary purpose was, and is, to make a cheap powder look polished. It also prevents clumping and will let it flow better. But the increased fouling make it a poor trade off in a propellant powder. "Black lead" was banned from propellant powders used by the British Military and surely ours as well.
If you look at Swiss the shine its not graphite, its polished. The shiny surface is actually Saltpeter that migrates to the surface during the final drying/polishing stage.
Swiss looks very much like the fine grained powder I saw in a 38 S&W revolver cartridge I pulled the bullet from some years ago. This powder in a UMC cartridge was not graphited. None of the high grade powders of the 18th-19th c were. We have to remember that the Moosic plant and the current plant at Minden make their real money from Military sales, not sporting powder. Moosic SFAIK never made any real sporting powder. But after Dupont destroyed the propellant powder industry in the late 19th-early 20th c buy buying companies and closing plants. When they were forced to divest only Moosic was making BP. The firms formed from the divestiture made smokeless. So when people talk about "quality" powder from Dupont or Goex from Moosic I have to chuckle. Once they stopped using boilers for heat and stopped using sterilized water in the powder (under Dupont) the powder quality got very erratic. Some on the later Moosic stuff was so bad I used to throw out 1/8 to 1/4 of a pound from every can since it was so dusty and full of "fines".
Minden is much better than the late Moosic powder for a couple of reasons, both more accidental than due to any effort by the
old management of Goex.
Dan
