In the 1800's, the British firm of ELY, used to sell pre-made shot ctgs for use in muzzleloaders. If you used paper-bag material, that should be stiff enough to hold the shot, and/or wads. I think they might not work for both shot and powder, but that's all part of experimenting/testing. You could glue the folded ends, or not, but treat them like a paper ctg. with powder and ball, shoving a wad down, tearing off one end and pouring the shot out of the ctg. or be totally contained.