These parts are designed to use a few solid layers on the bottom and then a continuous and unbroken profile all the way up the part. Prusa and Slic3r call this vase mode, while Cura calls it spiralize. I prefer Cura myself, since Slic3r gets a little persnickety about the bottom layers.

Thanks to Tyrant for pointing this out: For users of Prusa or Slic3r, they don't seem to appreciate the 0.05mm gap separating the lower half of the cylinders on the default 'Slice gap closing radius' setting. This setting is found in 'Print Settings' > 'Advanced' > 'Slice gap closing radius'. If you set this to any value below 0.02mm the model should slice properly.

Make friends and intimidate them with stupid-silly firepower why not? I've seen a few designs here and there for inline clips and I finally put a couple hours into my spiralled cylinder to get half darts stacked and firing.

In brief: the back dart is loose in the cylinder while the front dart is lodged and sealed in the front of the cylinder. When you pull the trigger, air pressurizes around the back dart and uncorks the front dart, leaving the back dart behind. Point the muzzle towards the earth to lodge the back dart in the front, and now it's the front dart.. so pompous and full of itself.

Most of the time, the back dart seats into the front of the cylinder without the help of gravity and you've got 16 rounds without a pause. Currently, the design does require the removal of the Hammershot's air restrictor. When the back dart becomes the front dart there's no dart to trigger the restrictor.

I can highly recommend taking a look at Ehdrien's designs and specifically their Inline Clip for the Nerf Nockout for an explanation on inline clips. They have a very helpful video explaining the mechanism of action. I promise I'll add a remix once Thingiverse fixes the remix search.