This is my second version of the original single shot shell. This should allow for depression of all air restrictors (on the stock gun) and works great in my modified sledgefire. They printed fine in PLA and the gun has much better FPS (I plan to build a chronograph soon for measurable results).
Check out my other designs for a standard 3 shot rear load sledgefire shell. If there is any interest in a two shot version let me know.
Print with the base at the top to allow for a better seal (if you are printing on a glass bed you can likely get away with printing it right side up but will need to remove the support in a few spots which may be annoying.