Go pick up some Triple Seven or Pyrodex if you can't get any real black powder. You can use 5-10 grains of 4f down the tube then load with the sub powder. By all means don't use a full charge of 4f down the tube or your just asking for a face full of shrapnel or your hand blown off. You can blow up a gun quick doing stuff like that and hurt yourself or people near you. Don't take a chance like that.
I also wouldn't recommend that you borrow any powder from anyone; who knows what they have.