Sadly,
@Wisconsin Relic only needs powder for the hunting season and the expense of ordering real black powder online is really quite unreasonable for small quantities. He can get by with Pyrodex or 777. These perform better with the use of a hotter percussion cap and nipples designed to deliver more flame to the powder charge. The substitute powders are designed to replace real black powder on a volume basis. So, use the volume measure to dole out the powder charge. The magnum caps (CCI #11 Magnum or RWS 1075) may be hard to find, but they will produce more flame through the flash channel. Hot Shot, Red Hot or Spitfire nipples should be available. I hope that he seeks out other shooters and can share an order to obtain some real black powder.