This is from 1998 edition of Dixie Gun Works catalog.
"How to load black powder blank shotshells.
Black powder is used in factory loaded blank shotshells, and should be used in handloaded blanks also. FFg granulation is recommended,
Either paper of brass shells can be used. The inside diameter of bress shells is greater than of paper shells,requiring special over size wads which are available. Also brass shells should be scrubbed in soapy water with a bristle brush after firing to remove black powder residue which would corrode them.
10 gauge blank shells are loaded with 6 to 8 drams of black powder.
12 gauges are loaded with 6 drams of black powder.
16 gauges with about 4 drams of blak powder and 20 gauges with about 3 drams of black powder.
It is absolutely necessarythat you use an extra heavy wad over the powder.
Either use commercial wads or newspaper carefully packed in tight.
Seal the wadding into place with Canadian Balsum or glue or candle wax."