Pre-packaged charges in aluminum foil are the most widely accepted method for firing cannons.
Disclaimer: Most of the things I recommend for firing cannons apply to bores 3/4" and larger, but .69 is close enough to the line that i feel it should be treated as a cannon . The rules for cannons are different than black powder firearms.
For .69, get a 5/8" dowel and use it to form a tube out of heavy duty aluminum foil. Pinch, roll, and press down one end tight against the end of the dowel to form a cup. (The edge of mine is rounded already, it's the handle of a powder ladle. If yours has a sharp edge you should round it off some.)
Pour your measured charge (this one is 60 grains) into the cup and pinch and fold the excess tube over. This your powder charge. When you ram it home, make sure it's tight against the breech face, and use a vent pick to pierce the foil.
These foil packets will work as blanks (with black powder), or behind an
unpatched ball.
The little mortar is there to verify the packet that I made would in fact fit down its .69 bore properly. I don't have a cannon in .69 to experiment with.