Do any of you guys remember the old Skeeter Skelton story about this? It seems he left powder in a hopper for a period of time then loaded some handgun rounds. This was when he was in some sort of law enforcement and responded to an accident with some injured livestock. Some of the stock needed to be destroyed so Skeeter began shooting only to have his cast bullets bounce off the skulls of several cows. He determined after further investigation the plastic in the hopper had an effect on the powder. This article was "Skeeter's Cow Killer Loads" if I remember correctly, very funny and a long time ago.