The Nerf Trilogy is a massive shell-loading, shell-ejecting pump-action 3-dart shotgun. I found other rival round shells, but they all seem to use just one massive hole in the middle or are missing the little side bumps so they don't fit well in the stock. 

This has three chambers to keep the air pressure high and reminds me of some sort of rocket part. 

Prints well without supports. Obviously the notches on the side are flat and curved so they don't print great, but it still fits just fine in the blaster. 

In theory this could work in the Shellstrike, which is a little handheld break-action shotgun pistol thing that uses the same shells, but then you're missing out on the complete unnecessary intimidation that is the Trilogy.