I purchased mine from GI Brass.
http://www.gibrass.com/gunpowder.html Below is from his webpage.
WC820 Orignal application is for the U.S. Cal. .30 Carbine Ball M1 round. This lot loads at 13.5gr with 110gr FMJ projectile. This is a ball powder which can be loaded using Accurate Arms #9 (AA#9) data.Perfect for .410 shotgun loads. This is pulldown ball powder. $56/8# jug.
Use the AA#9 data. A lot of shooters are using this. It works great. Here's a good place to read about surplus powders and ask questions:
http://castboolits.gunloads.com/forumdisplay.php?f=28
God Bless
Creeker