Penny Mortar

After trying to print this off as-is, me and my father noticed a few things that can be improved upon. We decided it would work better if we made it so the penny's case couldn't be easily pulled out of the arm's ridge. We also decided to add a stopper at the end of the arm so that there would be less variation when shooting. Please look at the original for instructions on building, because I think I tied the rubber band wrong.