The cowboy shooters also use black powder blanks to break balloons. I wanted to do the same thing for some fun shooting in my backyard, but I don't like cleaning up after black powder. So my solution was to use a charge of smokeless powder, and fill the rest of the case up with uncooked grits. Crimp a cardoard wad over the top and it works great. It's as loud as a regular round, but has almost no recoil, so the kids could enjoy shooting it. It will shred a cardboard box at contact distance, but will not even pop a balloon past about 20 feet.
Other than that I tried some wooden wadcutters out of a 357. They weighed about 10 grains or so, and I was getting almost 2000 FPS out of them. I have no idea what they could be used for, it was just a "will this work?" sort of deal.