Single-end Shells for Nerf Pilot

Edited a shell by [dddmkr](https://www.thingiverse.com/thing:6255440) to only be loadable from one end and to be a bit longer to fully hold the dart.

I prefer using shells that can't be backloaded, so you have to remove the shell every time to reload— it changes the feel a lot and is much more fun imo.

Works great in my stock pilot. My [barrel attachment lug](https://www.thingiverse.com/thing:6667076) comes with a couple clips for holding these shells for faster reloads.

Because the bore is cylindrical, old, worn darts may slip out due to being slightly too skinny. I might make an updated version someday with a tapering bore, but it really isn't that big a problem considering most blasters have trouble firing old darts.