I got a sledgefire with no shells, so I tried 3d printing this shell. It kinda worked, but shells had a poor fit in the chamber and wouldn't eject properly. I changed the size and shape of the fins to more closely match genuine Nerf shells, and made the tighter section in the bottom of the shell less dramatic in order to protect my darts from being smushed.

In my limited testing, it seems to be firing about as good as the originals, but I don't own a chronograph or anything like that.

I am currently working on variants of this shell such as an Elite slug, Mega slug, and Rival shot!