The aluminum charges I have seen worked fine. When you pick through the touch hole can you feel the pick go through the foil? And does the fuze, if used, go into the charge? The one I helped fire was loaded with the aluminum wrapped charge, the vent was picked into the charge, and the fuze was pushed into the hole in the charge. Worked well.
Find a cylinder shaped form that has a smooth surface (like a drinking glass) that is somewhat smaller than your bore. I made a wooden form the correct size and then drilled a large hole through it lengthwise (will explain the hole in a bit). Wrap the form with two layers of foil with enough excess foil protruding from the end of the form to fold up and make a bottom for the foil cup you are making. Carefully slide the aluminum cup off the form (the hole allows air through the form, otherwise you have to remove the foil cup slowly so it doesn't collapse as you pull it off the form). Put the cup on a scale and pour in the charge you want. Twist the and of the foil closed. I make my charges smaller than bore diameter so when I ram the charge home the foil cup will burst. Prick the vent and you're ready to go.