My son wanted some targets for his soft air guns. There are some designs here on thingiverse, but all of them take quite long to print if you want to have them a little bit bigger. This one solves the issue - just print it and put an old CD in the slot. Printing time for one is about 10 minutes on my K8200, and you can make a whole bed full of them in about an hour.
Print it an snap / hot-glue an old CD inside.