This is a remix of Nerf Sledgefire Shell by 3dYeti. I made this to be more accurate to the actual nerf shell. I added the small pieces slightly blocking the back end, as well as the small shafts inside that hold the darts. This has now been tested, the model needs some tweaking. When you open your nerf sledgefire to load a new shell, you will see some pins on the side opposite the barrel.

The shell has bee tested. Results are below.

The placement of the bars in the back of the shell makes it so that the pins do not fit correctly, so do not force the sledgefire closed with the shell if it doesn't close easily. You may damage your gun. I'm going to edit and test the model, but for now just shave a millimeter or two off of the bars across the back holes. TL;DR